I've collected a lot of data in an spreadsheet, and come to the following pricing averages:
EUR/Ah
- Cheap lead-acid (200 cycles): 1.6
- AGM lead-acid (400 cycles): 2.3
- Premium AGM (800 cycles): 3.2
- LiFePO4 (2000 cycles): 5.86
But when adjusted for cycles, the LiFePO4 is a clear winner, with the only disadvantage being up-front capital cost for a battery that must be used for 5 years to recover the investment:
EUR/1000 Ah cycles
- Cheap lead-acid: 8.13
- AGM lead-acid: 6.65
- Premium AGM: 4.51
- LiFePO4: 2.93
And when you additionally consider that the effective Ah available in lead-acid are only half, the prices above actually double.
In addition, LiFePO4 benefits from:
- very fast charging
- low SoC doesn't harm the battery
- higher discharge voltage means more Wh
- smaller volume and weight for equivalent
My batteries are cheap deep cycle lead acid.
Circumstances:
- Full-time boondocking with very rare access to 230VAC. I'd rather disconnect load for a few days and let the MPPT charge the batteries completely than pay "docking" fees.
- Alternator provides up to 80A, but as voltage rises, the lead acid batteries are unable to absorb the current (needs higher voltage for fast charging, but even at 15.5V they only absorb 3A each, despite being at 1.22 specific gravity, probably because they're sulphated)
- Generator is not an option: too bulky, too expensive, too noisy, too inefficient (fuel/kWh)
- Gas fridge sucks for true boondocking: no leveling is possible
Thanks for the advice though.
The problem is that the lead-acid batteries simply don't absorb well enough.
Also, since I drive daily, using the alternator for charging would recover 70A x 20min = 23Ah (20Ah effective, maybe)