Sakura/Erato/E-fun SLA to Lithium battery upgrade

Some headway 38120S 10Ah LiFEPO4 cells

Set of parts for one pack. 2 plastic trays, 12 cells, Either 5 plates (2 with holes drilled) and 7 straps or 6 plates (3 with holes drilled) and 4 straps, 2 main terminals and 5 BMS monitoring terminals.
(The plates need to be drilled to go over the 'legs' on the plastic trays)

Cells trial-assembled into plastic mounts. The +ve ends are just slightly too big and have to be forced in. This can break your plastic if you aren't careful. It's best to remove the shrink-wrap on 5mm of the +ve end as that make the diameter just right again.

Original K-long 36Ah Sealed Lead-Acid battery (12Kg) on the right, new 30Ah (4S3P) Lithium Iron Phosphate (4.5Kg) on the left.

Trial fitting of new battery back to check it physically goes in the space. You could get 5x3 cells in here, but not using these plastic mounts - their spacing makes it about 2mm too big.

The shrink-wrap has been removed on the +ve ends so they fit properly.

Headway connecting plate made of plated copper. These don't have quite the right spacing for use with the plastic mounts so each one needs the holes reamed a little so the bolts fit comfortably.

Pack made with kosher headway mounts for bottom half (legs hold terminals nicely away from the floor) and DIY top half.

Due to not being sent enough yellow plastic mounts I got to manaufacture my own from an old chopping board. Carefully mark centres (40mmm spacing, extra 5mm round the edge) then use a 1.5" hole saw which just makes a perfect 38mm hole if you are careful. note the messy trial holes where I wasn't careful.

I use a drill press to enable accurately vertical drilling and set it to stop when 2mm from coming through. Then drill again with 1 1/4" hole saw all the way through.

Cut off the excess

And with a dremel or knife (Knife was easier) remove the excess plastic so you get a nice stepped hole which stops the top cover sliding down with vibration over time.

And make 3 more (2 pictured here). Takes all afternoon.

Finished set of 4 assembled 4S3P packs

Getting the packs in involves taking quite a lot of the bike to bits so it's not easy to get them out later, so I did all the BMS wiring now even though I don't know what connectors will be used. Make sure all the bottom bolts are tight too - you don't want them rattling loose.

The moped battery compartment as supplied. (Take a phot so you know how to put it back together!)

After removing the seat bucket, remove 2 screws at the bottom front and take out the front-of-seat plastic piece. You will need to remove the resetable fuse too (not fitted here on all models) Then remove the 2 screws on the inside holding the front on the upper coloured trim on. But first the lower trim has to come off.

Next remove the trim piece below the rear light (2 screws). This exposes some more important screws.

To get the rear light cover off you need to release a clip at top centre. thin screwdriver works well. Removing this is not needed to get into the battery compartment.

Undo this machine screw on the side atthe front of the lower rear grey plastic trim.

And remove this screw half way along lower rear grey plastic trim.

And remove the screw at the back of the lower rear grey plastic trim (exposed by removing the trim under the rear light).

Now the whole lower trim piece can be unclipped from it neighbour at the front and then moved backwards a few mm to release all the clips, then moved downwards and removed.

It took me quite some time to work out that this lower bit needed to come off before the upper pieces could.

The rear coloured trim left, right and central pieces all needs to come off as one, because it is screwed together from inside. Remove this screw on both side to release the rear.

A naked moped, so now you can actually get at the batteries enough to remove them. The seat cross-bar has been removed too. There are two connections to each of plus and minus. One high-current pair for the motor via the controller, and one pair for the rest of the machine (charging, 12V electrics and controller low-power side). Keep tabs of the wires when you disassemble. Insulate things to avoid shorts.

This is the battery box with two of the old batteries removed. Getting them out is _really_ hard work because they are stuck down with double-sided foam tape, and there is almost no wiggle-room. Once you've got one out it get a bit easier. I had to slide a thin steel underneath to help cut the foam.

New lithium batteries fitted, and wiring connected. Note use of foam padding to accomdate slightly smaller battery packs, and protect cells from steel box.

Close-up of fitted batteries. By putting them in with + and - at the same ends as the old cells I could re-use the existing interconnects. NOte how all the unused BMS wires are taped-up to avoid shorts.