Enginer kit with Deep cycle batteries

...I should have mentioned recharging PHEV battery when dead & with Enginer kit turned off. I realize whatever is doing the recharge while driving is also using gas, that is why I say creatively/efficiently...

 

BMS2 will only work with a Prius Gen2. It can use a 230V lithium pack add on that connects directly in parallel with the Prius OEM NiMH battery pack. It can also use add on NiMH packs. It will not work with a Kia Hybrid. The main advantage that Enginer kits have is that they can be fitted to just about any Hybrid.

 

I'll add my voice to those recommending against lead acid. A lot of work was done 5-7 years ago on prototyping Plugin conversion strategies with SLA batteries. They were a relatively cheap way to experiment, but range was disappointing due to reduced effective capacity at high discharge rates, and cycle life was very poor. 6 months was common. When you factor in replacement costs, the initial apparent cost advantage evaporates. With the price of lithium packs now there is no real way to make a case for SLA being cost effective. You can find a lot of the early info from the open source cal cars prius plus project here:
CalCars' PRIUS+ Plug-In Hybrid
PriusPlus - EAA-PHEV
I believe the BMS+ and Plugin Supply conversions more or less grew out of this early work.

 

When using lead acid you also have to remember the batteries effectively have less capacity the faster you discharge them due to a non-linear effect known as Peukert's Law.

Peukert's law - Wikipedia, the free encyclopedia

As an illustrative example we can use the BB EVP20-12 battery used in the cal cars conversion. These are nominally a 20Ah battery, but the nominal ratings are given at a low current resulting in a 20 hour discharge time. In this case that would be 1A. Using Peukert's Law and the battery's calculated Peukert Number of 1.146, we can calculate the following effective capacities for various current outputs:
10A = 14.3Ah
15A = 13.5Ah
20A = 12.9Ah
40A = 11.7Ah
60A = 11.0Ah
100A = 10.2 Ah

At the kind of discharge rates needed for EVs and even PHEVs the effective capacity of your batteries can easily be half what you think its going to be. To keep cycle life at all reasonable you'd have to limit yourself to 50% DOD, cutting the capacity in half again. The same battery is specified for 600 cycles at 50%, and 300 cycles at 100%. Because of the poor energy storage density, the cal cars packs were often run pretty much all the way to 100% DOD adding to the poor life span, and still the range was disappointing.

The same would be true of a lower voltage pack with a dc:dc converter. Now instead of a 240V pack putting out 15A, you have a 48V pack putting out 75A. Assuming you scale the batteries for constant capacity you'd be pulling that 75A from a 100Ah battery, putting you at the same relative discharge rate as 15A from 20Ah. In reality you'll probably be slightly worse off with the dc:dc converter due to its inherent less than unity efficiency.

Its also worth noting that this battery was chosen from many candidates studied for the best balance of cycle life, cost, internal resistance and Peukert Number. Many other lead acid batteries will do worse in one or more of these regards.