Some technical Qs about e-bikes.

WIAWSNB

Q1 - batteries. I understand these have built-in BMS circuits to monitor and protect them during charging. After they have been charged and installed on the bike, is it then purely the +&- contacts that do the job? Ie, the bike's electronics work out the charge state for the display, and doesn't have any particular comms with the battery's electronics? If so, that means any battery of the correct voltage can be used, and connected via just these two wires?

Q2 - any recommendations for generic replacement batteries with down/seat/frame holder?

Q3 - LCD displays/controllers - are these 'standard' too? Ie, provided they have the same connector, such as the 'green' round 5-pin jobbie?

Thanks.

On-the-coast

Q1 pt1 maybe, maybe not. Could be designed either way. Pt2 not really, 2xpp9 batteries in series would give you 18v for example but wouldn’t move anything substantial.
Q2 - can’t answer

Q3 almost certainly not.
In general it’s a Wild West (or East) for e-bike design. Almost certainly one or 2 design houses and manufactures are going to making the majority of stuff so you might get lucky with comparability.
BUT you’re more likely to burn your house down with a battery / charger fire than you are to get lucky with retrofitting unknown stuff.

WIAWSNB

Cheers.

Well, I bought the bike… And - blimey - it's a barely-used Carrera Subway-e, needing only a new controller and a battery. The owner was understandably annoyed with Halfords that they didn't warn him to keep a charge in the battery… 3-year old bike, 3 short trips, and cost him £1.2k.

twopenny

I'm guessing they didn't warn him because a lot of rechargeable batteries need to be kept charged.

They really don't like being left on empty or very low for any length of time.

But yes, a reminder would have been good at least in the instructions that would come with it new.

WIAWSNB

Discovered the bike uses its own Suntour CAN-bus system, so - of course - the wee display is silly money, and the battery off the scale. I had a good idea it would be the case, but wasn't certain.

Exploring options, but the bike itself is pretty nifty…

WIAWSNB

Looks like the bike was worth the risk.

It needed a new CANbus display, a battery charger (which he hadn't mentioned, but "it's in the garage somewhere - I'll let you know if I find it"), and - potentially - a new CANbus-handshaked battery. Off-the-shelf prices are around £149 for the display, £70+ for the charger, and well in excess of £400 for the battery, with no alternatives available due to the specific Suntour CAN.

The former was sorted by finding a cable-chopped one on Fb Marketplace that the guy was willing to post - £25 - and I just spliced in the cable from the broken one that came with the bike. Found the correct charger on 'Bay for another £25.

The battery, well… A 'mare to open the case, but finally managed without too much damage. All looked good inside. The output from the output socket was absolute zero, which I guess is no surprise since the battery switch would not fire up, and the voltage across the actual battery bundle inside was just under 4V, so as deed as a deed thing.

Wired up a charger (a proper ebike type of the correct voltage, but with a straightforward DC plug on t'end) to a couple of metres of cable so I could place the charging battery out of harm's way, and also plonked a meter across the terminals to monitor the voltage. Plugged it in. It started at just over 6V, and climbed steadily over a half-hour or so to 9, 13, 24, 33…, and then it crept up more slowly. Kept monitoring for temperature, but all seemed fine.

Disconnected and left it overnight, and started again the next day. Voltage - over an hour or so - climbed to the mid-30's, but still no 'life' from the battery - no LEDs, no response. Disconnected the directly-wired charger, and plugged in the correct 'house'-DC-plug charger into the proper battery socket, and - blimey - charger started working, and voltage continued to climb very slowly. And then - yay! - the first battery level LED came on! This must have been at the high-30's voltage.

It must have taken another hour or two, but finally all LEDs lit, and the charger said, 'Green - I'm done'.

Pressed and held the 'on' button, and it fired up, giving 40-something volts out the socket.

Now to test it all on t'road - wife at helm…