3P13S x 18650 tubular battery pack - Balance charging / cell protection options
I am looking to build an 18650 battery pack to power down-hole well equipment. It will be either 3P13S or 3P14S to supply 48V at 5 A max. The pack needs to fit into ~ 1.5 in tube therefore the batteries need to be stacked. The plan is to have 3 in parallel arranged in a triangle, then 13 or 14 of these stacked in series. The resulting length will be over 3 ft.
I want good cell protection and the ability to easily balance charge without removing the batteries from the capped and sealed tubular assembly. I think that a 1.5" internal diameter will be to little to allow for an off-the-shelf BMS that could fit and meet my requirements. However maybe battery protection for the many cells could fit inside and I could have an external balance charger with a multi-pin connector that would mate to the tube assembly.
Does anyone have opinions or guidance as to what BMS/balance charger and separate protection circuits may work (and fit)?