12v NiMH Motorcycle Battery

OK, stop, hear me out first!

This battery is not intended for daily use. Its intended for use with a motorcycle which is in long term storage (years). The motorcycle will be kick started a couple of times in the year to help keep the engine in running order. It doesn't have an electric starter motor, so just needs enough power for the electronic ignition, to generate a spark.

For everyday use a lead acid battery is perfect, as it can handle overcharging (by boiling off) and can cope with the many charge cycles much better.

Ok so why not just buy another lead acid battery? I have done so in the past, but they don't like to be left discharged for long periods, and then usually die a slow death without a maintained trickle charge.

So rather than buy another new lead acid battery, I thought Id try and make a NiMH battery out of some spare batteries. I'd rather save buying a lead acid battery for when it comes back into road use. I might even try running it with rhe Nimh pack first to see how it copes, as its usually only ridden a fee weeks in the summer.

Why not use Lithium Ion batteries, you may ask? LiIon batteries don't take kindly to overcharging, and I don't intend to change my regulator to match it for a LiIon battery. I want to keep my motorcycle in its original condition. Having a homemade overcharged lithium ion battery, sitting next to a petrol tank is not a good idea.

Why use NiMH batteries, you may ask? Because I have enough NiMH batteries from a pair of old drill batteries (replaced by Lithium Ion batteries) which could be recycled for this application. NiMH can handle overcharging better, and they don't have a tendency to explode. It will also save the NiMH batteries from landfill, so a win for the environment too.

So lets give it a go, "garage54" style!

I started out by hacking the old lead acid case, but later found a suitably sized case in my stash of enclosures. The ready made case was better for easier accessibility to cells should they need to be replaced at a later date. I also liked the see through lid.

If you go down the hack lead acid case route. Full precautions need to be taken, gloves, eye protection, skin protection etc. I let the battery acid drain, then left it submerged in a bucket of water to dilute any remaining acid.

The top of the battery was cut cross-sectionally using a hacksaw. The old battery plates were persuaded out by whacking the case against 2 spaced blocks of wood. To remove the internal cell compartment walls, this was done using a combination of multi-trimmer, dremel and long nose pliers.

Good NIMH batteries charge up to 1.4v volts then sit around 1.2v.
My old nimh batteries would charge to 1.4v but then sit around 1.1-1.2v..
Rather than chain up 10 batteries in series (10x1.2=12v), I decided to chain up 11 batteries (11x1.2=13.2v) to handle the overcharging better.

The batteries were soldered in series using a soldering iron, and then soldered to a DC 2.5mm socket. Polyester padding was added to fill in the void space. Watch the cell polarities red/green sequence is highlighted in blue.

The batteries were charged up using a nimh charger.

Hook up the battery, ignition on, we have power.

Gave it a kick and it didn't start !
Checked the spark plug externally and it was firing, so batt was good.
After giving the carb a thorough clean, it started.

Monitoring the voltage, it peaked to 13.6v even when revving the engine hard, as the regulator kicks in.

I dont like keeping old gas fuel in my tank, as it starts to gum up, as the volatile additives evaporate, and hardens to a varnish and cause more problems. Eg foul the carb jets, sticking petcock valve etc.

As an interim measure I have hooked up a temporary syringe as my mini fuel tank. The syringe has the rubber stopper removed as it swells up with petrol. Its hooked up to the carb with some see through tubing and a fuel filter.

Watch this space for updates on how the battery holds on to its residual charge. If need be I can always plug it into my solar shelf charger.

It was good to hear the 2 stroke kick back to life after 4 years sitting silent with a dead lead acid battery. Where theres a will, theres a way!