Enginer Dc-Dc converter current inc?

You’re right Scott, the efficiency of the whole system (including losses the charger, fans, heat in converter etc.) is probably much less. There’s no way of calculating until I receive my new BMS. But there’s an easier way to find out what the overall efficiency of the whole system is. In an email Jack sent me in the past it shows that it will take 4.6 kWh to fully charge including several trickle charge cycles. The battery packs charge to 98% and discharges to 20% SOC.

On a full 4 kWh system only 4kWh * 78% = 3.12 kWh is used. Since 4.6 kWh is needed to charge from 20% to 98% and the depletion over the same range is known the efficiency of the system can be calculated as 3.12/4.60 * 100 is around 67.8%.

So your estimate was pretty much spot on. We could do some complicated calculations and maybe adjust a few decimals but it will still be somewhere around 68%. It would probably even differ a little with every individual kit.