Retrofitting Li Ion into a Giant Lafree (VRLA) battery

[90Ninety]

So I fancied tinkering with a new Ebike , I didn't wanna pay a lot since it would be my first . I picked up a Giant Lafree , for £40 , it actually had been hardly used and comes with all the old paperwork . Little did I know it had VRLA Acid Lead battery , the original pair it came with ( now dead ) , 2 x 12V in Series
My idea was to swap out the battery anyhow , I have already taken out the lead cells , and have found Lithium 24V that will fit nicely .

I could also change the charging circuitry ( shown ) by just jerry rigging a lithium charger brick inside . However I am debating if it maybe worth using the charging circuitry that is in situ .
I have read mixed experiences when using regular lead acid chargers on lithium batteries . Though Since the Lithium pack has own BMS , I am wondering if its worth a try before I rip the old circuitry out .

 

[Deleted member 4845]

The charging profile for lead is very different than the charging profile for lithium.

Improper charging is the #1 cause of ebike fires, and subsequent property loss and death.

The correct voltage for a "24V" lead battery is different to the correct voltage for a "24V" Lithium battery. Just for starters, did you choose 6S, 7S, or 8S? There are no such options for lead. If you chose 6S, then a Lead charger will dangerously overcharge your Lithium, in addition to not using the correct CC-CV profile.

 

[90Ninety]

Do you wish to elaborate further on the charge profile ? The battery has already successfully charged twice already , I have been monitring it so far , and its been ok , charger is getting only slightly warm as it would with Lead Acid.

The voltages for AGM and the Litium are actually within tolerances , AGM 14.4 V x 2 ( 28.8V ) and Lithium 29.4V . Though there is actually a adjustable resistor that allows + 2 / -2 V anyhow .

The only issue I noticed so far is the charger takes a little longer to detect the Lithium cells , due to its lower resting voltage .