RV Electricity – Just Ask Mike (J.A.M.): Can I swap in a lithium battery?

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By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.


Dear Mike,
The sales guy at the local RV shop tells me I can just drop in a lithium battery to replace my pair of old Trojan lead-acid batteries, but I’m suspicious. Is there anything else I should check to make sure this works? Can I replace two 6-volt batteries with a single 12-volt battery, and will it give me more power, as this guy suggests? —Derick

Dear Derick,

Well, you’re half right. You can replace a pair of 6-volt batteries that were wired in series to make 12 volts with a single 12-volt battery, no matter what its chemistry (flooded cell, AGM or lithium). The power question is just a bit more complicated since you can discharge each of these battery chemistries to different levels without damage. But you’re also missing one important item on your checklist before you pull the trigger on this purchase and write the check – that’s battery charging profile.

That’s because each battery chemistry has a slightly different voltage and current rates it likes to be charged at. Go with too much current for too long and you’ll boil the sulfuric acid and water out of a flooded-cell battery and ruin it. Not enough voltage fed to a lithium battery and you’ll never be able to get it fully charged. And the latter is the potential problem with simply swapping in a lithium battery in place of a pair of flooded-cell lead-acid batteries.

It all comes down to what brand and model converter/charger you already have in your RV. Many of the modern ones from Progressive Dynamics and others have a switch setting on the controller board marked something like LI for lithium. If your converter has that switch, then you should be in business.

However, if it doesn’t and its technical manual doesn’t mention a lithium battery setting, then you won’t be happy since it probably won’t charge your new (and expensive) lithium battery to much more than 75% capacity or so. And since you’re asking the power question, I assume you want more usable power, not just expensive bragging rights.

Finally, on that power question, note that modern lithium batteries can be discharged down to 0% of capacity (flat-lined) without damage, so 100-amp-hrs of lithium battery is good for around 1,2000 watt-hrs of power. That’s because 100 amps x 12 volts x 1 (full discharge) = 1,200 watt-hrs. However, a standard flooded-cell battery should only be discharged down to the 50% level or you’ll kill it rather quickly. If you have a 12-volt, 100-amp-hr battery it can provide only half that amount of power. That’s because 12 volts x 100 amp-hrs x 0.50 (percentage of discharge) is only 600 watt-hrs.

In your case a pair of 6-volt batteries with a 225-amp-hr rating will provide around 1,350 watt-hrs of power (because 12 volts x 225 amp-hrs x 0.50 = 1,350 watt-hrs). So you would be losing a little bit of total watt-hr capacity with a single lithium battery. However, if your converter/charger has a lithium setting and you could afford to put in two lithium batteries, you would now have a whopping 2,400 watt-hrs of usable power.

So you need to do a little more homework to determine if you also need to change out your converter/charger, and if you can get by with a single lithium battery or need to put in two of them to get the power you’re wanting.

Hope this helps your decision process and doesn’t damage your checkbook too badly….

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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18 Comments
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Larry347
1 month ago

Bought 2 Lithium batteries from Costco, then found I need to spend more money on a converter/charger upgrade that has a lithium jumper. Battery company recommended dc to dc charger to protect alternator. Still working on cabling on where to put the dc-dc charger and how to protect everything. Also, apparently lost the ability to start RV from house batteries. Must carry a portable power unit for jumping, now.

John T
1 month ago

There’s no such thing as watt-hours of power. The watt-hour is a measure of energy.

BadWolfe
1 month ago

Thank you for this article. I have to comment that it’s not just the fact that different types of coach batteries confuses me, its also the different maintenance requirements… Wet Cell, AGM, Lithium. Then, needing to watch the charging vs discharging levels (only use 50% of the 12 volt power on a Wet Cell battery means watching the voltage until it drops to 12.3volts?)

Tommy Molnar
1 month ago

One of the downsides for me, concerning LiPo batteries is their problems with cold weather. There are charging issues in freezing temperatures, and use issues as well. I’m sitting on the sidelines watching this new technology roll out, and watching other’s experiences with them before I fork out the substantial cost for a couple of these seemingly game changing batteries.

Stephen Kight
19 days ago
Reply to  Tommy Molnar

LiPo batteries can usually accept a charge down to 25 degrees at which time they automatically won’t accept a charge. You can mount them inside the RV to keep them warm and some come with heaters built in. Lead acid technology has similar temperature restrictions without the Lithium benefits. The technology is pretty much perfected now, so get off the sidelines and enjoy camping more.

Brad Teubner
1 month ago

Rule of thumb is to not discharge any lead-acid below 50%. I don’t know how AGM compare to flooded, but it is nice not to have the corrosion on the cables and battery box.
This is what DEKA says about their AGM
Depth of discharge/Cycles to 80% Capacity
10/3200
25/1200
50/500
80/250
100/200
I don’t know of any RV system that protects the batteries from a deep 12V draw.
(Other than inverters will shut down on low battery voltage.)
This is what Victron says about their Lithium
Depth of discharge/Cycles to 80% Capacity
80/2500
70/3000
50/5000

Last edited 1 month ago by Brad Teubner
Bruce Bon
1 month ago

How much can you discharge a top-of-the-line AGM battery, such as the Lifeline GPL-4CT. I am planning to buy a pair of these, for 220 amp-hours, but if I could only get 110 amp-hours without damaging the batteries, I might reconsider.

Also, will a typical RV power center/charger allow you to discharge the house batteries to a damaging level? My 2014 Navion has a Schumacher control center 94-026-866W that charges at 55 amps.

Brad Teubner
1 month ago
Reply to  Bruce Bon

Rule of thumb is to not discharge any lead-acid below 50%. I don’t know how AGM compare to flooded, but it is nice not to have the corrosion on the cables and battery box.
This is what DEKA says about their AGM
Depth of discharge/Cycles to 80% Capacity
10/3200
25/1200
50/500
80/250
100/200
I don’t know of any RV system that protects the batteries from a deep 12V draw.
(Other than inverters will shut down on low battery voltage.)
This is what Victron says about their Lithium
Depth of discharge/Cycles to 80% Capacity
80/2500
70/3000
50/5000

Wayne
1 month ago

Part of the cost of a well designed lifepo4 battery is the battery management system (BMS). It prevents battery damage from overcharge, undercharge, charging below freezing, excessive current draw. Lithium run about half a volt higher so things run a bit faster/brighter, charge much faster, are about half the weight with a noticeable gain in useable energy. Even the cost may less than FLA if the life span is as long as advertised. Time will tell. I installed them using the standard charger/converter and it worked fine. I have since installed a lithium charger to take advantage of the faster charge rate if I need to use the generator. My solar controller was programmable so it didn’t need replacing. Lithium batteries don’t need to be vented so I gained a little storage space where the vent hose was. Also, the battery terminals don’t corrode. If you like to boondocks lithium batteries solve many problems.

Cam
1 month ago

What about the alternator charging the lithiums underway in a motorhome?? There’s no lithium setting on that! Can drop in’s take that?

J Graham
1 month ago

In addition to updating the converter/charger, a DC-DC charger designed to charge the lithium battery from the alternator at the correct charging and float voltages should be considered, whether or not the vehicle has a smart alternator.

Don
1 month ago

The red flag here is “The sales guy at the local RV shop tells me…” Many sales folks know next to nothing about what they’re selling, and will say almost anything to make a sale. Talk to a technician about any new system you’re interested in…

Chris K.
1 month ago

Brad (Teubner), you are absolutely right! LFP battery life is certainly reduced if routinely discharged to 0%. LFP battery life is also shortened by routinely charging to 100%. TV alternators can be overheated and even destroyed when repeatably subjected to sudden load drops imposed by the LFP BMS. If that’s not enough, LFP battery life is also reduced as the recharging rate increases. Particularly disturbing is the LFP battery life reduction associated with temperature swings, most notable as temperatures rise above ~90 F. These issues are all documented and a good place to start online LFP research is at Battery University. The bottom line is simply that LFP batteries ARE NOT “simple” drop-in replacements for LA batteries.

LFP batteries certainly have advantages over LA batteries. However, these advantages can be completely lost without proper design and operation of the LFP battery bank. That can very well leave the uninformed with a large holes in their wallets!

Brad Teubner
1 month ago

Mike, check the data sheets from the drop-in manufacturers. For example ReLion says that battery life is around 1/5 if 100% discharged compared to 50% discharged. Also, charging at full auto alternator voltages is reportedly very hard on them. Also issues with large current draw from the alternator overheating the alternator and the battery-charged-hard-disconnect damaging the alternator. In any case, I have disconnected the alternator from the Lithiums, only charge with solar or shore where both the charging systems are set to 13.6V max.
So I charge to 90% and discharge to 20%.
Basically my 220Ah useable, 280lb of Leads were replaced by 280Ah useable, 130 lb of Lithiums. The big advantages I see of Lithiums is that they are more compatible with solar charging (not absorb or float voltages where they don’t utilize full solar) and they don’t mind (actually prefer) partial charge.

Tom
1 month ago

Mike, Had the exact same question in my mind. I really like the idea that you can run a Li battery flat without destroying it. I have not found information on my Xantec about switching over to Li. After paying $1K for battery, replacing current charging system in not in the cards.

Cheter Brede
1 month ago

Mike. You need to read up on LiFePo4 batteries. I find this series of white paper worth a read. http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

WEB
1 month ago
Reply to  Cheter Brede

Very good reads, just in time for the winter hibernation!

BadWolfe
1 month ago
Reply to  Cheter Brede

Thank you for this link. Very good article.