Bigger is Better: Battery Lessons on the Road

Bigger is better; in the case of batteries for overlanding. 

In the planning process for building out our battery and solar system we found there is a lot of information out there, but little that applied and that was relevant to our situation and charging capabilities. Each system is unique to your own power needs and uses, but here is the story of our experiences and what we would have done differently.  **Disclaimer - We are very aware that these systems are far more complex than we have expanded upon. There are many sites that explain the nitty gritty in far more detail than we have included.  We just wanted to share our experience and what would have been useful to know before we built our system.  

Our van came with a group 34 dual battery set up and 90 amp alternator.  The dual battery system is in the engine compartment under the passenger seat. There is very little wiggle room to change battery sizes, so we searched for group 34 AGM’s with the highest amp hours available that would fit in our small space. As for solar we searched for 100 watt panels that had the highest efficiency per solar cell and weight.   The alternator being stock for a dual battery system, we assumed would be able to charge both batteries when driving. While that may be true for very little discharge, there is a governor of sorts that reduces the charging amperage after a few minutes of driving to be a constant 3-4amps. This is not enough to recharge a battery with significant discharge.  A battery charger built into our IBS system would have even able to charge the batteries at a higher amperage until full. We didn’t know that was even an option before starting this journey. Most posts lead you to assume the alternator is enough. It can provide enough juice, but there needs to be a mechanism to draw more amperage otherwise it will default to where the governor is set.   

Here is what we initially installed:

1. Two 65 amp hour Northstar group 34 AGM batteries
2. One 100 watt SunPower Flex Panel (Click here for the write up on our solar setup)
3. MorningStar SK12 Charge Controller
4. IBS Dual Battery Monitor
5. Victron Battery Monitor - BMV-702
6. 12 gauge wire for all house wiring (except for wire to fuse panel)
7. Blue Sea Fuse Block 
8. Blue Sea 12V and USB outlets
9. Blue Sea Dimmer for LED’s
10. We also have a Goal Zero lithium ion Yeti 400 that has 40 amp hours as another power source in the van.  The inverter is broken and the two USB ports don’t work so essentially it is only useful for one 12V socket.  After the whole battery failure and fridge failure situation, we now run the fridge on the Goal Zero during the day when we drive while it is charging via an inverter and switch the fridge to the house system at night. This way the house battery can get a full charge while we’re driving without a constant draw during the day.   

Our daily electrical usage consisted of the following:

We wish we could say the initial setup we installed worked like a gem, but we can’t.

Here’s what happened:

Initially, we installed two 65 amp hour group 34 AGM batteries from Northstar.  One was our house battery and one was our starter battery. Both were installed in the original location of the existing batteries; in the engine compartment. The regional rep assured us that these batteries would be perfect for our application, energy use and charging capabilities.  We disclosed to him prior to purchasing that we had one 100 watt solar panel that has a max charge amperage of 6.3 volts; more likely 4-5 due to daily weather and temperature conditions. We have the 90 amp alternator while driving from site to site. We also provided our original energy use calculation chart (see above for those calculations).

We installed the IBS dual battery system to connect the house and starter battery when driving and to disconnect them when parked. Hindsight has shown us that we really needed to install a battery charger into this set-up because the alternator alone will not charge at the amperage needed to bring the house battery to full. After the initial engine start, the alternator charges at an average of 3-4 amps.   IBS has a battery monitor with a charger, but it didn’t occur to us that we would need one. We assumed the alternator would take care of it. In our research of how other people set up their battery systems we never encountered a built in battery charger. Lesson learned.

Another interesting feature that we didn’t anticipate with the IBS is that it will connect the two batteries when the solar charge is higher than 13.5 volts, thus reducing the voltage going into the house battery. When charging in full sunlight the solar charger produces 14-14.8 volts.  This definitely had a negative impact on our first Northstar battery because it never was able to get the full charge potential from the solar panel. It was being shared between two batteries instead of just going to the house battery. Since then, we have found an override to manually disconnect the batteries so that when we are parked in one place for a while the only battery getting the charge via solar is the house battery.  The only downside is that if we forget to re-link them before driving to a new spot the house battery will not get any charge from the alternator. At this point though, we rarely forget as it has become a habit to check it everyday.

Originally, we estimated our daily amp hour usage to be about 25 amp hours or the equivalent in watts at around 320 watts. So in theory we would need AT LEAST 4 hours of full 100 watt intake on the solar panel to recharge the battery everyday. That’s in theory, the reality is that the panel brings in (on good days) 60-80 watts per hour. So we really needed at least 8 hours of solar charging on bright sunny days to recharge our daily usage of 320 watts.  A key factor that we overlooked, was the required amperage to recharge the battery. It’s not just simply how much the solar can produce; it's also a matter of the current at which it can charge.

Once we started our journey south, we learned that the fridge was using three times as much energy than the company claimed it would.  So our initial calculations of 160 watts of daily use was drastically different from the actual 450 watts of use. This really put our battery use beyond the 50% depth of discharge safe zone.  After two months on the road we were pushing our daily discharge to 50-55%; meaning we were using 36 hours of the 65 amp hour capacity when we should have only been using 25-30 amp hours ma. That made it quite difficult to get a full charge between the solar and alternator. We had a couple of cloudy days whilst exploring Baja and low and behold the house battery took a dive for the worst.  Our charging system simply did not have the capability to bring the battery back to a full charge. However, this was not the only reason our house battery failed as we came to learn from more digging and research.

We found out, while in Loreto, that these Northstar batteries need a much higher recharge amperage than our system could provide. So not only do they need a higher amperage to charge than our system was capable of providing, our fridge was consuming way more energy than we anticipated. After contacting IndelB on numerous occasions during that first two months to find out what was wrong, they finally admitted that their website data is not accurate and that the fridges use more than they claim online.  Buyers beware!

Once we were able to get Northstar on the phone, the regional manager informed us that these batteries require a bare minimum of 12 amps for recharging and their ideal range is 20-40amps. Why is this? Northstar has designed their batteries with super thin plates; thus creating more surface area. This allows the sulfates to form on the plates faster than would a traditional AGM with thicker plates.  To counter this sulfate formation they found that the higher amperage charge rates are able to break up these sulfate formations. No surprise then that the Northstar house battery failed in a little after two months on the road. Our solar charging system at 6 amps was not enough. Surely he could have told us that information in the beginning before we purchased these batteries. Luckily, the starter battery is fine because the depth of discharge is so little that the alternator can recharge with higher initial amperage (13-21 amps) in a short amount of time.

Discovering this in Loreto was a bummer because it was so bloody hot (95F) and we could not use our fans or fridge. Sleeping in Peso was out of the question so we quickly left the Sea of Cortez and made our way to the Pacific side to San Juanico.  Before we left Loreto, we found a place to “super charge” the house battery as per the instructions of the NorthStar representative at 40 amps for 8 hours to try and revive the battery. It took a lot of convincing of the shop to recharge it this way. They thought we were crazy.

While we were in San Juanico (land of very slow wifi and no cell service) we contacted VMaxTank batteries and found an 85 amp hour solar battery that would fit in our space and required only 5 amps from solar for recharging.  At this point on the journey, we couldn’t justify the work it would take to install and reconfigure the space for a bigger battery. Otherwise we would have installed a 200 amp hour battery. (Note** another concern was the added weight of the bigger battery. We feel that Peso is maxed out on weight so we didn’t want to risk adding an additional 100 pounds for an AGM. If we build another rig we will definitely skip AGM and go with lithium ion). We ordered the battery that would fit and had it shipped to La Paz. We also ordered an additional 100 watt and 50 watt flex solar panel from SunPower; weighing in at less than 6 pounds. The extra 100 watt panel fits nicely under our mattress and the 50 watt panel fits behind the bench seat.  We thought about roof mounting the new 100 watt panel, but we love being able to move it around in the sun when we are camped for a few days in one spot. We use the 50 watt panel to charge the Goal Zero.

The moral of this story is that bigger really is better.  We highly recommend getting a battery with an amp hour capacity that will discharge only to 80% after your daily usage. This will increase the life of your AGM and it will charge faster and more efficiently.  We also recommend installing it away from the engine compartment due to heat and accessibility.  The factors that led to our battery failure were complex and multifaceted. It was a hard lesson to learn on the road. There are more factors such as engine heat that we didn’t address in this write-up, but we are aware they exist.

In hindsight, for our current set-up we would have purchased a bigger AGM house battery and installed it under our bed compartment. (However, for a future build we would choose lithium ion. We will refer you to Tucks Truck for more detailed information on lithium ion setups. It is more complex and requires a bit more detail than we are able to provide you with here.)

A bigger AGM house battery (in the range of 200 amp hours) would have been beneficial for a number of reasons:

1. Our daily draw is around 30 amp hours. The ability for a 200 amp hour battery to recharge on a 100 watt solar panel during a sunny day is much faster and efficient than the same draw on a smaller amp hour battery.  This is because of the level of the depth of discharge and how batteries recharge. We would only be discharging 70-75% rather than 50% every day.
2. If we had some cloudy days, the battery would be able to handle the extra draw without going below the 50% depth of discharge. With our initial battery set-up, one cloudy day was enough to go beyond the 50% depth of discharge unless we ran the alternator to recharge it.  This scenario, while it doesn’t seem like a big deal, is not ideal when you’re parked in a place for more than a couple days.
3. If we needed to use more power than planned in a day, the battery would be able to handle it.
4. The battery should last longer because the number of life cycles increases as you decrease the depth of discharge. For example the battery we have now is estimated to have about 1000 life cycles at 50% depth of discharge. Whereas the same battery at only 75% depth of discharge has 1800 life cycles.
5. The location under the bed system would have much less heat impacting the ability to recharge.
6. Our single 100 watt panel would be capable of bringing the battery to a full charge from 80% depth of discharge. This is due to the way AGM’s recharge.

Since we have adjusted our system, installed a new fridge and new battery, we haven’t had any charging deficits. It’s not exactly perfect, but it’s the result of making adjustments and changes while on the road.  The best advice we can give about choosing and designing your battery/solar system is to make sure you choose a battery that will only drop to 70-80% depth of discharge after your daily energy consumption. So if you use 50 amps per day aim for battery capacity with 200-225 amp hours.  The best solar panel is the one that is the most efficient per solar cell. There are more efficient panels than the SunPower Flex panels, but we chose to eliminate extra weight over the choosing most efficient. However, these panels are the most efficient we have seen in the flexible panel category.  The amount of solar you need really depends on how much energy you plan to use in relation to the size of your battery. Your battery capacity is the limiting factor to how much energy you can use and how well your solar will be able to recharge.

So, yeah a bigger is better in regards to house batterie. Feel free to ask questions or leave comments. We feel that we have learned a lot and would love to help others not make the same mistakes we did.

**Notes on why we would choose lithium ion:

1. You can discharge much lower without damaging the battery.
2. The rate of recharge is much faster and you can charge at a higher rate.
3. Weigh much less for the same amp hours.

It is important to note that a lithium ion setup is a bit more technical that an AGM setup.  We do not have the knowledge to guide anyone or teach how to set it up. However, as we said before we would go that route on a future build over AGM.