Any clue as to why regen is "smoother" on Lifepo4+SLA then..

[Sangesf]

Just lifepo4 alone?

I've noticed that when I'm using the brakes on a 36v 15ah lifepo4 and regen starts slowing me down, I get a (small) initial "jerk".
When I seried a 12v 36ah SLA to the lifepo4, the regen doesn't produce that initial "jerk", and I've noticed that the braking effect is not as pronounced (strong)...

Any clue as to why that is?

On a side note, a few months ago, when my BMS on the lifepo4 was "broken" (and didn't allow regen current INTO the battery through the BMS), regen would not work (no braking effect). Is that a normal occurrence to?
(All of this on a non-GM battery, but using Magic Controller)

[Hardcore]

the sla can't handle much amps, so if you put them in series the amps will go down and so will the power it's getting from the regen which will make the initial ''jerk'' disappear as you're not getting as much amps when applying the brakes.