Backup Battery Testing LiFePO4 vs. AGM

[rv6ejguy]

Well if we take my test at face value- around 11 amps draw for 20 minutes, the AH rating comes out to about 3.7.

Figuring in the degraded performance at the test temp of 8C vs. the usual rating temp of 25C and the fact that the battery would last relatively longer pulling out about half the current, these batteries might just deliver 6 amps for one hour at 25C.

As far as backup power for my EFI system current draw, I won't count on this one to last much more than 15 minutes and the identical primary battery about the same.

I want to be on the ground in less than 30 minutes after alternator failure if I shed all other electrical loads.

[McStevens]

That seems shockingly bad. Unfortunately most of the other info out there seems to be along the lines of "it starts my motorcycle/car so it's great!".

I figured these were too good to be true...

[judoka5051]

"Shockingly" bad. Ha!

[svyolo]

Shorai doesn't really explain it very well, or openly, but the info is there on their website. A different brand actually gives two ratings on their website, one the actual capacity, and the other "Pbeq". That means that used as a starting battery, their battery with a 6ah "capacity" cranks an engine as well as 18 ah lead acid battery. The Pb eq means "lead" equivalent.

Used as a starting battery, I can't argue with their salesmanship logic. We are using them as starting batteries, but also want them to act as a backup, which is a use for which they were not intended, or marketed.

Shorai's website doesn't do a good job of explaining this. EarthX rates their capacity at a 1C discharge rate. Another brand I saw had both a "Pbeq" rating, and ah rating, next to each other. The PBeq rating was 2-3 times the ah rating.

[rv6ejguy]

Originally Posted by McStevens

That seems shockingly bad. Unfortunately most of the other info out there seems to be along the lines of "it starts my motorcycle/car so it's great!".

I figured these were too good to be true...

2.2 pounds to start your engine is amazing however it doesn't compare in lasting power to a true 16AH AGM at 11 amps draw as the test shows. You can go up to a pair of the "36AH" model at under 5 pounds each which should give you an hour of running time. You can also look at other brands of batteries. I have the Shorai and wanted to test them and it would be great if people having other brands would perform a similar test and post their results.

You'd have to consider the cost vs. weight ratio here though as with all LiFePO4 batteries, they are not inexpensive.

[rv8ch]

Originally Posted by rv6ejguy

2.2 pounds to start your engine is amazing ...You'd have to consider the cost vs. weight ratio here though as with all LiFePO4 batteries, they are not inexpensive.

The other thing to think about is for your starter battery you need a fat cable (#2). Having that tiny lifepo4 near the starter is convenient. For an endurance battery, you can get by with smaller wires, like a #10. This makes it much easier to place the battery to help your CG, or at least not hurt it.

[gasman]

Why wouldn't you use a battery like this as a back up battery.......

Mighty Max Battery ML18-12 - 12V 18AH CB19-12 SLA AGM Rechargeable Deep Cycle.

[rv6ejguy]

Most any brand of 18AH AGM weighs around 12 pounds, take your pick...