Safe to recharge from battery bank ?

my lipo chargers keep dying and I have a 48v 20kw 500ah battery backup bank at home

how can I safely charge my batteries directly from that bank?

today I was desperate enough to disconnect bank and use the bank's charger with the smallest fuse I could find being 5A and charged my 13S e-bike battery from 50v to 54.4V which left it around 53v off the charger

any simple way to limit the draw from battery bank while its charging e-bike and set a cutoff voltage?

have been looking for adjustable Constant Current Buck Voltage Regulator but so far all i can find are up to 30v

No batteries are more simple to charge as RC lipo. They do require monitoring, but the lack of BMS and high charging rate tolerance are making them able to be charged with almost any kind of charger or power supply.

I bulk charge my RC lipo for years with Meanwell PSUs, at a very fast rate that is sometimes much higher than their charging C rate spec. Yet I never fried a PSU, nor set fire to a lipo brick. I am always present watching, that is the only condition. Most of the time I complete charging short of 15 minutes, sometimes as quick as 7 minutes.

If your chargers keep frying, it is because you buy sh*t or use them in horrible conditions. Just buy good PSU on the used or recycling market, and they will last much longer than your bikes.

Then, about charging a lipo battery from another lipo battery. You only need current limiting. That can be done as simple as using a cheap brushed motor controller, or any other mean of current limiting that you can build yourself with junk.

Brushed controller to limit current,, that's a cool idea. Those cost like 15-20 bucks. Adjustable.

I possibly should have mentioned 13s 18650 battery cells with BMS

but yeh looking for a DC Adjustable Constant Current Buck Voltage Regulator step-up that can have 48v input and does 48 - 90v output

something like this but step up

http://www.ebay.com.au/itm/DPS3005-LCD-Buck-Adjustable-DC-Constant-Voltage-Step-down-Power-Supply-Module-/162402290180?hash=item25cfee4a04:g:098AAOSwx6pYqqQp