Inside a Shorai LFX14L5-BS12 Lithium Starting Battery

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Oct 8, 2016
I picked up a lot of these small starting batteries recently. It's always fun to have a look at something different. These are typically used in motorcycles or small power tools for engine starting (hence the name). This one was the first I took apart. I was surprised to find pouch cells inside, but it makes sense given they often have a higher discharge current than cylindrical cells. The battery is dead, all cells reading 0V and they're rather puffed up.

Here's the battery on Amazon if anyone is interested. They sell for $128 brand new.

An interesting characteristic of these starting batteries is the power bypasses the BMS. This one does still have a BMS for balancing, but both positive and negative go straight to the terminal so it cannot shut down the battery if over or undercharged. This leaves some risk on the user to know how to properly design the application. I imagine heavy starting currents would blow out the FETs quickly.

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Oct 8, 2016
4s so i guess LiFePo4. They are often built like that where the BMS dont have any functionality to disconnect. This due to the added cost and also the self discharge it adds. LiFePo4 are very friendly in such case that they will tollerate alot of beating.

Valence do tha same on their 500-900USD 12 batteries. They have current monitoring but no disconnect. Only balance and monitoring.


New member
Dec 16, 2020
That is why I build my own for my Honda CRF150F. It only needs 80A to start so I used a Daly 60A continously discharge BMS with 120A peak. I used k2 power cells 2.85Ah from battery hookup 4s2p with a plastic battery case purchase on AliExpress. Works realy good and has overcharge and over discharge protection. Same size as Shorai. Total cost: 24$ for cells plus 30$ for bms plus 10$ case and 5 nickel strip= around 64$.