I'd like to start a thread that really discusses in depth what is known about these two battery
types and when each should be used. I want to start by providing a very good and in depth analysis of actual testing of both types of batteries.
An in-depth discussion (YouTube) of the actual chemistry and construction. Very good video.
From this what I know is that Lead Acid batteries (PbA) are useful for a very small handful of use cases:
1) Starting an engine. This requires enormous currents for a few seconds and then the battery
is immediately recharged by the alternator.
2) An RV where the owner always stays in parks with electrical
hookups. This allows the battery
to be charged back up if it is used at all during the day, moving around and sight seeing.
3) The RV already has a (dead) lead acid and the owner is getting ready to sell the rv. Let the next owner deal with the problem of a lead acid battery.
Lead Acid Batteries have several very real problems.
1) Their actual usable capacity is dismal
2) They require a full charge after use, every time. Not doing so will shorten the battery life.
3) The battery life is not good, anywhere from a hundred charge cycles if poorly maintained to around a thousand if well maintained
4) They weigh a ton. They are made of lead after all.
5) They do not come with a BMS. YOU are the BMS for a PbA battery
OTOH they are cheap, and commonly available.
LiFePo4 batteries have a couple of very real problem.
1) Charging them at temperatures below freezing will shorten their life.
2) Upfront costs are 2-4 times the cost of PbA
Otoh they have a ton of positives:
1) Their actual usable capacity is very high vs their rated capacity.
2) They charge very fast
3) They are very light
. A 100ah battery weighs about 30 lbs.
4) They come with a BMS (Battery Management System) a computer which monitors the battery and controls with an iron fist the charge and discharge of the battery, protecting them from most kinds of damage. This protects them from over charge, over discharge, over temperature charge and discharge and cold temperature charge (in some batteries).
5) They can easily provide gigantic currents. A 300ah battery may well provide 300 amps which will feed a 3900 watt inverter, for a full hour. Large RVs may have 1000 ah batteries and 1K or even 2K watt solar
and could actually run the AC on battery and solar
1) LiFePo4 batteries explode and burn down the palace. Not true. Lithium ION batteries do this, a different chemistry.
2) They are damaged by charging at low temperatures. Possibly true. Charging a LiFePo4 battery at a high current will cause lithium plating on the cathode damaging the battery. However trickle charging a fully charged battery does not do this. Some BMS systems prevent this. Some do not. Charge the battery up and flip the switch to disconnect the battery and prevent charging in cold temperatures.
3) Using the battery at a cold temperature damages the battery. Not true, although ALL BATTERIES have significantly less capacity at low temperatures
4) PbAs will provide 50% of rated capacity. Rarely true. See the link above for actual testing about this subject.
5) PbAs are not affected by cold temperatures. PbAs lose a lot of capacity at low temperatures, more that LiFePos in fact.
6) LiFePo4 do not self discharge. They do, about 2-3% per month.
1) PbAs are not useless. Owning one does not make you a bad person. They have been used for decades.
2) LiFePo4 batteries are in almost every way a superior battery.
3) LiFePo4 should NOT be used as a starting battery, in fact in general CANNOT be used as such. Their BMS will not allow the required currents.
4) LiFePo4 batteries do not care if they are charged all the way up, in fact would prefer not to be.
5) You should NEVER store a LiFePo4battery completely dead. They self discharge at about 2-3% per month and will discharge to below their safe capacity and damage the battery.
6) LiFePo4 can be stored for several years without a charger applied. Just be aware that they will eventually discharge too far and damage the battery. Charge them all the way up and disconnect the battery. Done.
7) LiFePo4 can charge at extremely high rates, often up to their rated charge capacity. That said, in the end the BMS itself controls the charge rate. A 100ah battery may or may not charge at 100 amps. Usually the BMS has MOSFETs which determine how fast the charge can happen. However it is not uncommon for a high capacity LiFePo4battery to charge at 100 amps or even more.
8) LiFePo4 can provide extremely high discharge currents, often up to a 1 C (or more) rating, i.e. at their entire amp hour rating. A 200ah battery might well provide 200 amps of current until the battery is drained. Again however this is determined by the power rating of the BMS.
9) a PbA can only rarely and only briefly provide their rated discharge current. A high internal resistance causes the voltage to drop fairly rapidly and the discharge current out to fall
10) Discharging a PbA at high current will cause an immediate reduction on actual current available out of the battery FOR THAT Discharge cycle. This effect is NOT permanent however.
11) Watching the voltage of a PbA is not a good way to determine if the battery is at 50%. At high discharge currents the voltage drops well below the recovery voltage. Thus the voltage does not reflect the discharge state except after a rest period.
11) The same is true for a LiFePo4 battery but for different reasons.
Battery type issues using Solar and Generator:
PbA requires a full charge as discussed above. The problem with PbA batteries is that their full charge cycle takes a looooonnnng time. It seems that it accepts it's amp rating (100 amps for a 100ah battery) for the first half of it's charge and then slows down dramatically. But it needs to be fully charged, so for several hours it may only be accepting 20 amps, then 10 amps, then 5 amps... as it creeps towards full charge.
So let's say that you have a solar setup with 600 watts. which puts out perhaps 50 amps. Cool, the PbA battery takes 50 amps for some period, then it slows down. Even though the panel has 50 amps available, the battery only accepts 20 amps, then 10, then 5 amps. Lots of solar power
just wasted, not stored because the battery cannot accept the current.
The same problem occurs with using a generator
to charge the PbA battery. A 1K generator
can provide 1000 watts or about 77 amps. The battery may accept that for a little while but then slows down accepting current. So you end up running the generator for many hours because the battery has to be fully charged but it is only accepting a small current for the last half of the charge cycle.
Contrast that with a LiFePo4 battery. These batteries can accept pretty much whatever the BMS allows, i.e. a 100 amp hour battery may take 100 amps. But it does so until the battery is about 90% charged before it too starts slowing down the current it accepts. So the 100ah LiFePo battery will accept 90ah in the first hour, i.e. charge to 90% in about one hour. Even the last 10 percent will only take another hour or so.
Which means two things. For solar, you can purchase a smaller solar array, and or it can fully charge the battery even when cloudy. For generators, a smaller generator will charge the battery many times faster. In addition to all that, the LiFePo battery simply does not care if it is charged up, or even what it's charge state is, OTHER THAN, not stored empty. If you run the battery down overnight and it is cloudy out, no problem, no charge. You might be inconvenienced but the battery doesn't care.
These specific issues make owning the two battery types very different in terms of maintenance. LiFePo4 is pretty much just maintenance free. Use it, charge it, use as much as you want, charge as much as you can but it won't kill the battery.
Just to be clear, neither battery chemistry will survive 6 months sitting in a dead charge state.
Connecting house to starting battery:
Connecting a PbA battery to the tow vehicle battery is quite possible and moderately easy. Add an isolator, run a couple of big cables and you're done.
Connecting a LiFePo4 to the tow vehicle battery is not recommended. The biggest reason is that the LiFePo4 can accept enormous charge currents, and can easily burn out the tow vehicle alternator. If you want to charge from the alternator, you should use a Dc-DC converter which is sized to the alternator.
Mixing battery chemistries
Don't do it. Putting the two typed in parallel is bad because they rest at pretty different voltages, and the PbA battery will pull current from the LifePo battery causing it to discharge. You absolutely can charge a PbA battery from a LiFePo but not vv. Just don't leave them connected together forever.
There is more to say on this subject but I think this provides a good place to begin the discussion. I am NOT trying to slam PbAs or people who have them and use them. I used them in my scamp
for many years. They still perform just as well (or poorly) as they ever did. It is simply a case of better solutions being now available.
Please do chime in with your own experiences. I know quite well that the vast majority of owners have only ever used a Pba and think they are just fine. And they can be just fine. If you only ever camp in parks with outlets then buying a LiFePo battery makes no sense at all. OTOH if you want to boondock, they make a lot of sense.
So comment. But let's keep it civil please.