Battery going dead.

I have a few bikes to choose from when I want to ride and as I only have one arse, by the time I get round to riding some of them the batteries can be very low, I have Podtronic type regs on most of them and they are wired straight to the battery.

There is a small current flowing through the regs which is draining the batteries and yesterday I started to do something about it.

I bought a few 40amp relays and started to wire them onto the bike as follows: (standard wiring top, relay added below)


I notice in another thread that the newer Nortons seem to suffer some parasitic drain and it occurred to me that this solution would work with them as well, by fitting the relay pins 30 and 87 into the fuse holder for the clock circuit, an inline fuse to the relay would replace the fuse removed for the relay connection. The clock would need setting each time the bike was used but that would be cheaper that replacing batteries.

Hi , I will try that , as some of my bikes suffer of the same problem even with Shindengem reg/rec , at a time JeanDr had measured those drains , may be Grant Tiller will chime as he is a geek about our Norton wiring ......!!!

Yes, a Podtronics regulator/rectifier draws just under half a milliamp when everything on the bike is shutdown.

The original zener doesn’t exhibit the same behaviour.


Not sure I’d want to rely on an energised relay coil to be be keeping my battery connected to everything else on the bike.

You could simply connect the reg/rec negative (black) lead to pin 2 on your ignition switch - you wouldn’t be switching high current, so you’d not be putting too much load through the contacts on the switch.



Just my thoughts, of course.

where's the fuse?

maylar said:

where's the fuse?

Click to expand...

After the load arrow.

gtiller said:

Yes, a Podtronics regulator/rectifier draws just under half a milliamp when everything on the bike is shutdown.

The original zener doesn’t exhibit the same behaviour.


Not sure I’d want to rely on an energised relay coil to be be keeping my battery connected to everything else on the bike.

You could simply connect the reg/rec negative (black) lead to pin 2 on your ignition switch - you wouldn’t be switching high current, so you’d not be putting too much load through the contacts on the switch.

View attachment 18705

Just my thoughts, of course.

Click to expand...

The relays seem to be quite reliable, I use them on a headlamp harness I made without problems. If the relay packed up on a ride it would be simple to bypass the relay.

storm42 said:

After the load arrow.

Click to expand...

If the fuse was at the battery where you show an ammeter (normal wiring) you could simply pull it out after a ride. Tape it to your seat for next time.

The fuse should go between the battery and the ammeter on your diagram.


Yes I get your point that relays are very reliable - there’s one thing using one for a horn (sirens and flashing lights on the Interpol) or a lighting circuit if you want to use a more powerful lamp but something else altogether using it across the whole bike.
It’s just not my cup of tea if there are alternatives.


If you take a low spec battery like the Yuasa YB9B - it’s capacity is 9ah

So with the current draw of a Podtronics, it will take over a year to drain the battery to half it’s capacity.

If that’s an issue, just stick it on a tender every six months.


Or if you want to switch the parasitic drain out of the picture, stick it the other side of your ignition switch and treat it like the other consumers on the bike.

Putting the regulator on the switched side will not work because you won't be able to turn the bike off. With switch off It will run off the regulator alone without the battery.

The kill switch still cuts the ‘hot’ feed to the ignition.

That would work.

maylar said:

If the fuse was at the battery where you show an ammeter (normal wiring) you could simply pull it out after a ride. Tape it to your seat for next time.

Click to expand...

I could, but that would soon knacker the fuse holder, plus it would be a pain on some of the bikes, my way is fit and forget automatic.

gtiller said:

The fuse should go between the battery and the ammeter on your diagram.


Yes I get your point that relays are very reliable - there’s one thing using one for a horn (sirens and flashing lights on the Interpol) or a lighting circuit if you want to use a more powerful lamp but something else altogether using it across the whole bike.
It’s just not my cup of tea if there are alternatives.


If you take a low spec battery like the Yuasa YB9B - it’s capacity is 9ah

So with the current draw of a Podtronics, it will take over a year to drain the battery to half it’s capacity.

If that’s an issue, just stick it on a tender every six months.


Or if you want to switch the parasitic drain out of the picture, stick it the other side of your ignition switch and treat it like the other consumers on the bike.

Click to expand...

It isn't across the whole bike, it is just disconnecting the regulator from the battery, the rest of the bikes wiring is, including their fuses, untouched.

That wiring diagram is from the Podtronics website, I have just added the relay to it, I don't have any ammeters.

There are 5 bikes in my garage with Podtronic regs on them, the parasitic drain kills the batteries, 2 last year. I do charge them but it is such a minor mod, I see no downside to it.

Also, I have a diesel van and it has a relay that when pulled from its mount stops the engine, the van is 10 years old and the relay has never given any trouble, relays are used in many cars and critical to the engine running, so I don't have a problem using one in a position that would just stop the bike from charging, If the relay did fail it would just be a matter of pulling the relay and bridging the the socket in the appropriate place.

I have fitted relays to 3 of the bike now and after being left for a few days, all the batteries are sitting around 12.6 volts, I know it hasn't been long but the Norton would have been lower than that by now.

Another benefit of the relays is there is now no need to disconnect the battery to charge it, if for some reason it needed charging.

gtiller, I see you use the Shindengen 775A reg, did you notice if the bike seemed to have more power when you started using it?, I seem to remember rally drivers would disconnect their alternators for special stages because they thought they took more power to turn when connected. I am guessing that a shunt reg shorting the alternator would make it harder to turn and an open circuit reg wouldn't, is it noticeable?

Get yourself one of the new 'smart chargers' and leave it on the battery all the time. I've had one on my bike since I bought the AGM battery back in 2005 and it still registers 12.7V and will start the bike. It won't last long however, the battery is too old. But they do work and keep the battery in the best shape you can expect. I use them on my Miata which is notorious for bad replacement AGM batteries and my JD 2020 with 2 large lead acid batteries to start the diesel. Batteries last a lot longer with these smart chargers. That's been my experience and I'm sticking with it. I must have about 6 of them and all the batteries are old but work. What usually wears out is the connections with the battery acid. I've also got a B&S generator that must be 12 years old now and is still on the original GEL cell.

I have used the Optimiser chargers, and two different ones killed batteries over a winter layup, I have a friend that found the same, he came up with the idea of using a standard battery charger connected to a timer which switches on for 20 minutes a day, he hasn't had to replace a battery since.

I now have two CTEC chargers and they are much better, but I had a CTEC fail on a generator at work and kill the battery so even they are not infallible. There is also the worry about leaving these small chargers plugged in unattended when there is over £50ks worth of bikes in the garages, one of which is joined to the house, not unknown for charges to catch fire. I have a Seeley lead acid/Lithium charger/maintainer which seems very good, not the cheapest but I felt the need for the lithium battery on the race bike.

Anyway, all subjective now as the relays are working for now and I will probably fit another 2 today. What got me thinking this way was my little Aprilia SR50 scooter, the battery on that is minuscule and the bike sits outside under a cover and only gets used as a paddock bike once a year, I have owned the bike 7 years and it has never failed to start on the button and I have never had to charge the battery, I don't know what kind of charging system it has but there is zero parasitic drain and the battery is still good. (of course now i have said that, it will need a battery now)

@storm42 yes, the car boys have a different set of issues to deal with than us.
Typically with an alternator that has field coil(s) the overhead in terms of drag is much larger than we see with our permanent magnet types.

Our alternators pose only as a 1/2hp overhead and run at about 50% efficiency - so much better than the 30% efficient modern automotive type!

I see no parasitic power drain with the original Zener or the Shindengen units that I like to use (compared to the 0.5mA of the Podtronics short-type unit)
There must be some, but it doesn’t register either on the Fluke nor my analogue AVO (which is far more sensitive)

Our forum friend @Jeandr noted similar behaviour during his testing, which you can read about here:


In terms of noticing anything, on the bike - no, I haven’t.
Off the bike, I can spin the rotor inside the stator significantly easier than when I cross the output wires together.
Furthermore, an open circuit runs a cooler stator than when the wires are shorted out - even on a lathe at comparably less RPM than when on the end of a Commando’s crankshaft.

I don’t have the kit to measure that kind of thing, but I would be very interested to know.

storm42 said:

I have fitted relays to 3 of the bike now and after being left for a few days, all the batteries are sitting around 12.6 volts, I know it hasn't been long but the Norton would have been lower than that by now.

Another benefit of the relays is there is now no need to disconnect the battery to charge it, if for some reason it needed charging.

Click to expand...

I think your relay mod is a viable method of disconnecting the parasitic load. It only adds about 150 milliamps when energized.

Just a quick update on this thread, I put the meter across the Norton battery tonight and it measured 12.4 volts. It has been the best part of 4 months now since I last used the bike and I have not had a charger on at any time, it has been cold round here of late too.

I would say that the relay mod has been a success because the battery would defiantly have been flat without it. I will try and check the other bikes I have fitted the relays to tomorrow and post the results.

Production dates on all batteries ?