Lithium for dummies: need advice in simple terms

[profdant139]

I have been torturing myself, trying to develop some sort of a decision tree to see if I should convert to lithium batteries. I have searched the archive for a "lithium for dummies" thread and have come up empty. (If I'm wrong, I am sure someone will let me know! 😉 )

So that is what I am humbly asking for -- is there a really easy to understand site or article that explains or compares lithium batteries to lead/acid batteries for RV use and then guides the shopper through the steps needed to come to a conclusion?

Or maybe this thread can serve as a resource for those of us (like me) who do not have technical backgrounds?

In any event, here are my particular questions:

Aside from the obvious cost difference (which may or may not be a deal killer), my three biggest concerns are weight, capacity, and cold weather charging.

Weight: I am in my eighth decade (!) and am having trouble lifting a group 31 lead acid battery without hurting my back. It looks like lithium is a clear winner on that issue.

Capacity: I'm satisfied with the capacity of a group 31 -- it's nominally at 110 amp/hours, which means I can get about 55 amp/hours from the battery without risk of damage to the battery. Am I correct in concluding that if I were to get a lithium battery with 100 amp/hour capacity, I could use almost all of that capacity?

Cold weather: What does one do about charging a lithium battery when camping in sub-freezing weather? We really like snow camping -- is that a deal killer? We are almost never subjected to temps below ten degrees. And the daytime usually warms up to around 30 or so.

Thanks in advance for your help and advice -- and on behalf of all of us dummies, thanks for keeping it as simple as you can!

[StirCrazy]

otrfun wrote:

theoldwizard1 wrote:
. . . What I don't know is if below freezing will affect the battery life while discharging or storing.

Specs vary from manufacturer to manufacturer, but generally speaking, maximum recommended discharge current tapers downward as temps drop below 32f or so. Probably wouldn't want to do more than a .10c - .15c discharge at temps below, say, -10c (14f).

Long-term storage recommendations are not too stringent. If you follow the temp recommendations for charging (typically 0-40c; 32-104f) that should be acceptable. If you want the absolute best for your cells, strive for 25c (77f) and 30-50% SOC.

the specs for the new cells I ordered are pretty good that way, 0.5C discharge down to -30C short term storage of a month -40C/F long term storage -25C and charger from -5C to +60C. but it totaly does depend on the manufacture and for premades, they tend to add a little more of a buffer so they have less warenty clames they have to pay.

[Veebyes]

As a former boat owner my boat was kept on a revolving mooring, no connection to shore, no solar to maintain the battery bank. It would sit unattended for weeks, months sometimes, with no charging. The boat was dead. Nothing but a bilge pump hard wired to the battery.

Never had a problem. This experience is not unusual. People such as farmers & construction companies leave machinery unattended for months at a time.

This with wet cell batteries which self discharge much faster than AGM, gel cell or lithium.


Read the manufacturers instructions on care & follow them.

[otrfun]

Veebyes wrote:
We buy lithium AA & AAA batteries, stick them in a drawer & don't get around to using them for months, years even, take them out & they are just fine.

Ditto. Just found some Energizer AA lithium batteries stuffed in a box with a Garmin GPS we used for off-shore excursions on the east/west coasts years ago. They're almost 10 years old and still measure 1.82v! When new, I believe they measure ~1.87v. Amazing.

[theoldwizard1]

Veebyes wrote:
We still have the wet cell battery mentality that somehow the battery is going to go dead if not left on a trickle charger or, heaven forbid, left disconnected & unattended for a month or more.

Based on anecdotal evidence, I know believe that lead acid should NOT be left on a trickle charger 24/7 for multiple weeks. Plug your charger/maintainer into an cheap mechanical lamp timer and only charge for about 4 hours per day.

Veebyes wrote:
We buy lithium AA & AAA batteries, stick them in a drawer & don't get around to using them for months, years even, take them out & they are just fine.

Very different battery chemistry. You are trying to compare apples to oranges, although they both have a very slow discharge rate.

[3_tons]

pianotuna wrote:
profdant139,


find a timer that allows one hour of charging per 7 days.

find a charger that does the "float" voltage for the particular Li chosen.

The biggest parasitic load on Li is the battery management system.

While it’s natural to entertain ‘off the cuff’ pontifications from the (serial confused?) uninitiated, a far better plan might be is to stick to the ‘learn-ed’ advice from actual LFP users - ‘scheduled’ LFP charging of any kind should be avoided, as its only applicable to wet-cell experience…Once in electrical isolation, any parasitical BMS loss is quite minuscule (if even determinable…) over a time, in fact the isolated LFP can rest for months on end with very little self-discharge - how much of this might be strictly attributable to just the BMS is in my view anyone’s guess…

3 tons

[Veebyes]

We still have the wet cell battery mentality that somehow the battery is going to go dead if not left on a trickle charger or, heaven forbid, left disconnected & unattended for a month or more.

The newer battery chemistries go for months with very little self discharging. I have been an AGM fan since before my RVing days. My trailer AGM battery sits disconnected & unattended from November to April. Come back to it in mid April & power is still there to run 5er landing legs.

We buy lithium AA & AAA batteries, stick them in a drawer & don't get around to using them for months, years even, take them out & they are just fine.

I worry more about unattended battery chargers & trickle chargers failing than I do self discharging of batteries over time.

[pianotuna]

profdant139,


find a timer that allows one hour of charging per 7 days.

find a charger that does the "float" voltage for the particular Li chosen.

The biggest parasitic load on Li is the battery management system.

[otrfun]

profdant139 wrote:
If storage at 50% state of charge is optimal, I guess I can't just put a lithium battery on a shelf in my garage hooked up to a BatteryMinder Plus (which is what I do now with my lead acid dinosaurs). Dumb Question Number 17 -- if I can't leave a lithium battery on a trickle charger, how do I keep it at 50% while it is in storage?

And by "storage," I mean "whenever I'm not actually on a camping trip, the batteries go onto the trickle charger."

Thanks to everyone for your continuing patience with my naive questions -- judging by the little "hit counter" on the welcome screen for this forum, there are a lot of other folks like me who are curious about lithium but aren't sure what to ask.

Lifepo4 *cells* by themselves have extremely low internal parasitics. We have a 200ah 3.2v cell that I removed from a cell pack about 10 mo. ago. Voltage of the cell at the time I removed it was 3.287v. Checked the voltage last week and it was 3.285v. At this rate it could a few years to drop to 50% SOC (~3.280v).

The BMS in a lifepo4 *battery* is tasked with protecting the cells 24/7/365, and, unfortunately, needs to draw power from the cells 24/7/365 to do so. Not all BMS's (or cells) have the same parasitic draw, so the rate of (self) discharge will vary slightly from battery to battery. For long-term storage purposes, I'd suggest charging a 12v lifepo4 battery to 50% (13.13v), disconnecting everything from the terminals, then checking voltage every few months. Log the voltage drop. After a couple of checks you should have the data you need to pick the best time interval for the following voltage checks. In any event, once the voltage drops to 13.00v (30%) suggest charging it back to 13.13v (50%) again.

As 3 tons and 2oldman have already mentioned, for storage purposes, no need for a charger (unless a recharge to 50% is necessary). Charge the battery to 50% SOC, then disconnect everything from the lifepo4 battery terminals. Make occasional voltage checks as previously mentioned. Important tidbit: leaving a charger connected to a lifepo4 for long periods of time (at 100% SOC) can potentially damage the battery. 50% SOC is the sweet spot for a lifepo4 battery/cell.

[2oldman]

Your Li battery doesn't need to be on a trickle charger. They prefer not to be kept at 100%

[3_tons]

“And by "storage," I mean "whenever I'm not actually on a camping trip, the batteries go onto the trickle charger."

LFP’s Uber low self-discharge rate makes the solution to this quandary easy…I simply added a battery ‘side’ post knife switch disconnect from Amazon which isolates the battery whenever camper is not in use…No need to keep on a trickle charger….In this way shore power (if available?) can continue to be used to operate the 12v systems via the onboard converter-charger…

[profdant139]

If storage at 50% state of charge is optimal, I guess I can't just put a lithium battery on a shelf in my garage hooked up to a BatteryMinder Plus (which is what I do now with my lead acid dinosaurs). Dumb Question Number 17 -- if I can't leave a lithium battery on a trickle charger, how do I keep it at 50% while it is in storage?

And by "storage," I mean "whenever I'm not actually on a camping trip, the batteries go onto the trickle charger."

Thanks to everyone for your continuing patience with my naive questions -- judging by the little "hit counter" on the welcome screen for this forum, there are a lot of other folks like me who are curious about lithium but aren't sure what to ask.

[otrfun]

theoldwizard1 wrote:
. . . What I don't know is if below freezing will affect the battery life while discharging or storing.

Specs vary from manufacturer to manufacturer, but generally speaking, maximum recommended discharge current tapers downward as temps drop below 32f or so. Probably wouldn't want to do more than a .10c - .15c discharge at temps below, say, -10c (14f).

Long-term storage recommendations are not too stringent. If you follow the temp recommendations for charging (typically 0-40c; 32-104f) that should be acceptable. If you want the absolute best for your cells, strive for 25c (77f) and 30-50% SOC.

[theoldwizard1]

profdant139 wrote:
No thanks -- I'm not going to build my own battery. My previous attempts at soldering have all ended up looking like abstract sculpture, and not in a good way. 😉

I might give it a try if I could assemble a battery using duct tape ?

Check out Will Prowse YouTube channel. He has several videos on building your own battery, even from bare cells. NO SOLDERING, but you do need proper crimpers.

profdant139 wrote:
But why not build a cozy box and conserve energy? Is there a downside that I am missing?

If your battery has a management system that prevents charging below 35°F, and you use thick (2"?) foam, you should be good. Discharging does create a small amount of heat.

What I don't know is if below freezing will affect the battery life while discharging or storing.

[StirCrazy]

pianotuna wrote:
Hi all,

Does anyone know if LiFePo4 are endothermic or exothermic on discharge?

With 25 f being the target, life gets a lot easier.

Exothermic, if it was endothermic they would make your campsite colder as they warmed up....

[Bobbo]

otrfun wrote:

Grit dog wrote:
^Another PT Barnum quote hidden in the above reply.

Insteading of being vague, why don't you specifically address the Barnum quote to help out the OP?

I think he is referring specifically to BB's high price. Consider it a Convenience Tax.