The base electrical system is shown with a choice of two battery solutions. This page goes over the pros and cons of each battery solution, and provides a bit info on keeping your batteries alive longer.
At the top level, Its really a pretty short story – the golf cart battery solution offers a much lower initial and lifetime cost than Lithium batteries for those who want to keep to a budget and don’t mind doing some occasional maintenance. The Li battery solution offers somewhat higher performance, a longer life, and less maintenance at a much higher price.
They are both good solutions – Which is the best for you just depends on your needs.
There are other battery solutions, like AGMs that we are not going to cover here.
The table below shows some of the characteristics for the two battery solutions shown for the base system.
|Two Golf Cart
|Two SOK brand
|Two 210 amp-hr, 6 volt
flooded lead acid
golf cart batteries
|Two 100 amp-hr, 12 volt
LiFePo4 Lithium batteries
|170 amp-hr (80% DOD)
|180 amp-hr (90% DOD)
|120 lb total
|60 lb total
|200 amps (BMS limited)
Golf Cart Battery Details
In the table above, nominal capacity is the name plate capacity of the battery. For most batteries you cannot use the full nameplate capacity and get a good battery life. Usable capacity is the actual capacity you can use and get a good battery life.
The golf cart batteries are 6 volt, 210 amp-hr batteries commonly used to power golf carts. Two of these are connected in series to make a 12 volt battery. They have been used a lot in camper van electrical systems for years. Because of their main use, they are readily available just about anywhere and prices are reasonable.
Life of these golf cart batteries if you take reasonable care of them is 5 or 6 years. Some people get as much as 8 years, and quite a few people get only a couple years because they don’t take of them – see maintenance below. Life time camper van cost is likely to be about $380 (2 sets – one set now and a 2nd set in 6 years)
Other positive golf cart battery points are very good tolerance to cold temperatures and no limits on cold temperature charging. They are pretty robust – they don’t require a sophisticated Battery Management System to protect themselves from self destruction as Li batteries do – although not taking care of them at all will result in rapid destruction.
When you combine these low-cost batteries with the rest of the Basic system, you can build a very capable and high quality system that does all the basics for $700. Sometimes looking at the discussions on the camper van forums these days, you get the impression that you have to spend $5K or $10K on your camper electrical system – you really don’t (but you can 🙂
Maintenance & Care- Golf Cart
Golf cart batteries require that water be added as needed – usually every few months. Takes about 5 minutes and gives you a chance to inspect the battery terminals and check for any sign of problems (something that should be done with any kind of battery).
Golf cart batteries need to be kept fully charged – especially when sitting idle between trips. If allowed to go to and remain in a low state of charge, they will have a short life. Solar charging can be used to keep the batteries at full charge between trips, or a quality battery maintainer (eg Noco) can be used.
For best life, lead-acid batteries should get an equalization charge once in a while. The charger in the base system will do this. A lot of people don’t do this and still get decent life.
For best life, a multi stage charger should be used. The chargers in the base system are multi stage.
Like any battery, the terminals should be inspected once in a while and cleaned and tightened if needed.
SOK Battery Details
The SOK batteries are 12 volt, 100 amp-hr Lithium -Iron-Phosphate (LiFePo4) that have become pretty popular with the camper van crowd. They are currently $570 each – half the price of a Battleborn (another quality Li option) and a couple hundred more than the cheapest LiFePo4 batteries on Amazon. Will Prowse and others have done tear downs and testing on the SOK and they appear to be built well. Searching the ProMaster forum for SOK batteries will bring up a number of discussions on it. I decided on the SOK due to the tear downs showing good quality, having low temperature charging protection, and the replaceable BMS. I think that the replaceable BMS does not get enough attention. To me, the BMS is highly stressed power electronics that may well have a much shorter life than the battery cells – time will tell I guess. If you can’t replace the BMS when it goes out, then the battery is useless even though the Li cells might be fine.
Life of these batteries in real life is hard to predict in that LiFePo4 batteries have not been in use long enough in camper van service to have a track record yet. The 3000 to 8000 cycle life specs are meaningless for camper van service, where you might only do 50 cycles a year – the battery will die of something else long before the predicted cycle life is reached.
Other positive features of the SOKs (and other LiFePo4 batteries): they have a very flat voltage discharge curve compared to lead acid – so, they can go from full charge to a low charge and the battery voltage hardly changes; little to no maintenance, although lowering the state of charge between trips is a sort of maintenance; and low weight – only 30 lbs a battery.
Lithium batteries with their low internal resistance can handle high currents better than lead acid batteries, but the SOK (and most other Li batteries) use a BMS to limit current to 100 amps per battery, which ends up limiting them to less than the lithium cells could do. But, they have a substantially higher maximum current capability than the golf cart batteries. If you plan to do lots of heavy loads (e.g. microwave), the LiFePo4 will handle that better. Of course, more battery capacity can be added to handle heavy loads better.
Maintenance & Care – SOK LiFePo4
LiFePo4 batteries are very sensitive to being operated correctly, but they have a built in BMS (Battery Management System) that takes care of the details of keeping all the cell voltages correct and protecting the battery from damaging by overloads, over temperatures, etc.
Like any battery, the terminals should be inspected once in a while and cleaned and tightened if needed.
LiFePo4 batteries must not be charged at temperatures below 32F. The SOK batteries have a temperature sensor that prevents charging at low temperatures automatically. If the van gets cold soaked in sub-freezing weather either before or during a trip, the batteries will have to be warmed up before charging – this will take a long time. Recently, batteries with internal heaters have become available – I would say the jury is still out on whether this will prove to be a good reliable solution.
LiFePo4 will deteriorate (lose capacity) slowly just sitting on the shelf. High temperature along with high states of charge accelerate this capacity loss. Leaving the SOK batteries at full charge parked in a hot summer location between trips is not good for battery life. I think its a good idea to at least lower the state of charge between trips to 70% or so, and if you are in a hot climate, it may be worth taking the batteries out and storing in a cooler location. There is really not enough history of use on the use of LiFePo4 batteries in camper van service to know how much of a problem this will be over time – probably best to be cautious.
Lead Acid Battery Myths
There is a lot of misinformation floating around about lead acid batteries these day. I think part of this is all the people who have become Li enthusiasts since Li batteries have become more practical and cost effective.
50% Depth of Discharge
Don’t discharge below 50% DOD (Depth of Discharge). In fact, lead acid batteries can be discharged routinely to 80% DOD. This does reduce the number of cycles you get out of them, but this is pretty much true for any battery chemistry (including LiFePo4).
The chart above shows cycle life vs depth of discharge for some Trojan lead acid batteries. The red line is the Trojan six-volt golf cart battery that is used in some camper vans.
At 50% depth of discharge, the golf cart battery has a predicted life of about 1200 cycles, at 80% depth of discharge, the life drops to 750 cycles. If you go through the math, the total energy you get out of the battery at 50% DOD is almost the same as the total energy at 80% DOD. In terms of total energy out, there is no penalty for 80% DOD.
As a practical matter, if you size your battery pack to cover your worst-case scenario (furnace running, little sun, heating shower water, …) for 80% DOD, then the great majority of your cycles will be much less. So, if you size the batteries for 80% DOD in the worst case, most of your cycles will be less than 50% anyway.
So, bottom line is that the golf cart batteries have a usable capacity of 80% of 210 amp-hrs, or 170 amp-hrs. A pair of LiFePo4 100 amp-hr batteries used to 90% of their capacity gives a usable capacity of 180 amp-hours – not much different.
They only last 2 years
The Li battery sales people tend to say this. In fact it’s easy to get 5 or 6 years out of a golf cart battery if you just take care of them a little bit. Some people on the ProMaster forum have reported that their golf cart batteries are still doing OK at 8 years.
The simple maintenance is 1) adding water every few months (or at least check), and 2) keeping the batteries fully charged between trips. Lead acid batteries die if they are not kept charged while the van is sitting in the driveway between trips – solar or a battery maintainer can handle this.
Much lower energy density
This may be true in an idealized sense, but, this has not proved true in any case I’ve looked at. Our base system suggests either two SOK LiFePo4 batteries or two golf cart batteries – both with about the same usable capacity. They also both have near identical volumes. This is also true of a couple other Li batteries I’ve looked at. The increased energy density does not seem to actually materialize with the current packaging.
Many say that lead acid battery compartments on a camper van need to be vented to the outside because hydrogen gas is produced during charging and it is an explosion hazard if not vented. I’m not convinced of this and the logic for this is laid out here… You can read it and decide for yourself.
I’ve had a ProMaster camper van conversion since 2014. Up until last year, I used the two golf cart solution and it worked fine. I had to replace the golf cart batteries once due to my stupidity – I let them discharge to empty by not cleaning the snow off the solar panels. Last year we switched to two SOK batteries as discussed above. I like them. Our first real trip with the SOKs was a couple months ago up to the Yukon. The SOKs performed flawlessly, but I was struck by the fact that we never did anything the golf cart batteries could not have done just as well. If I did not know the batteries were changed I probably would not have noticed the difference. I guess the message is, don’t write off golf cart batteries without having a look at them.