UKH

My motorbike has been laid up over winter, as is my usual habit.  It's been plugged in to a  battery tender which has worked fine in the 14 years I've had it but recently I've noticed that it's been showing the orange "charging" LED continuously rather than the blue "charged and monitoring" one.  I unplugged it and did a quick check on the voltage across the battery terminals and it looked OK - not brilliant but OK - at 12.5V.  Plugged the tender in and it stuck resolutely on "charging" again.

I took the battery out of the bike and connected it directly to the battery tender, which lit up its blue "all good" LED in just a few hours.  However, the voltage across the battery terminals was then ~11.5V which doesn't sound particularly healthy to me.  Putting it back in the bike and turning on the bike ignition the voltage across the terminals drops to ~10.5V which I think is so far from healthy as to be toast.

I'm resigned to shelling out for a new battery (it is ten years old which I think is pretty long in the tooth for a humble lead acid battery) but I'm just wondering whether the slightly odd behaviour of the battery tender might indicate that it too is on its way out.  I'd rather not buy a new battery and have it ruined by a faulty battery tender.  On the other hand, decent battery tenders seem to be quite costly - around about the same as a new battery - so I'd rather not splash the cash unnecessarily if the observed behaviour is consistent with a near-dead battery alone.

Anyone able to offer any informed advice?

Did you check the battery voltage immediately after removing the tender. If so, leave it an hour before checking.

It may also be corrosion build up on the battery lugs, if the tender is clipped on to the wire terminals. 

However ten years is a good run for a battery. 

Sounds like just your battery to me. However I'm a bit dubious about these battery trickle chargers.

I had my battery charger on for my two previous bikes, both ended up having a knackered battery.

Some of the chargers don't reach full trickle mode for about 11 days which means that's a lot of time for the charger to be charging at about 80% voltage. More so if you ride the bike in that time and start again.

At one point our car battery would charge quickly to full voltage and start the engine. The next morning it wouldn't start engine and would be low voltage, roughly 5/6ths of normal. 

Charging was a two or three hours rather than overnight you'd expect from battery capacity and charger current.

I think one cell was knackered (low capacity so quick charging, also overnight discharge) and the other 5 cells were OK.  

Lead acid 2.2 volts per cell, 10.5/13.2=0.795 which is not far from 5/6ths.

Your might be something similar - you now have a 5 out of 6 cell battery due to age?

Correction - battery age, not your age

Had a similar problem, thought it was all kinds of things until I bought a Tester and used it to check the battery before, during and after charging, and then again after I'd started the bike up (having taken it off charge.

Basically the battery was losing charge pretty quickly, and whilst it would start the bike up first thing in the morning after taking it off the overnight trickle charge, it was the devil to start up again to get home from work.

Got a new battery and the problem was sorted. Still using the Charger with no problems.

Ten years it's probably just knackered, motorbikes don't have the most sophisticated charging systems and the batteries have a miserable life.

Treated one of my steeds to a new li-ion batt this winter, below zero it was completely worthless and ended up re-fitting the old one for the winter!

Had that on my old motorbike battery - my Dad had access to a proper tester at the time and that said it was a bad cell and new battery required.

Ended up fitting it in a supermarket car park on the way home from picking it up, after I stopped to grab some bits on the way past and the bugger wouldn't start again.

Last time I had similar it was the charger. I found out after I had bought a new battery. 

Thanks all for your advice and experiences.

At ten years old, and on the principle that two volt meters aren't both lying to me, I'm happy to replace the battery.  (The terminals were a bit gunged up, although the tender was connected by screw tags directly to the battery, not via croc clips.  It was after I cleaned the terminals and connected the tender up on my workbench using croc clips that it started saying that he battery was good when all other evidence suggested otherwise.)

I am struggling to understand why the tender thinks it's fully charged, though.  Which means I'm reluctant to leave a new battery at the mercy of what is now a suspect battery tender.  On the other hand, my experience is that a battery left un-tendered usually fails a lot sooner.

Does it help at all to simply disconnect the battery if the bike's likely to be laid up for a significant period of time?

When the battery is old it gets sulphated (like a crust covering the plates) which stops the electron transfer into the plates so they take no power from your battery charger and it then says it's fully charged even though it isn't.

If you actually had an amperemeter in the circuit you see the demand from the battery drop to almost nothing in minutes.

I think you have five OK cells in series with one bad cell, a bit like 5 cells from a diesel lorry in series with one cell from a moped. The bad cell charges to full voltage. It's quick because the bad cell has low capacity. The tender sees that the voltage across the whole battery is in the right range and indicates fully charged.

Unfortunately the bad cell does not hold it's charge.

I think you are one cell short of a full battery!

The battery has lasted ten years. That's twice as long as the I'd expect. The battery tender seems to have done a superb job. It seems more likely that the battery  just died of extreme old age

I'm no expert, that's just based on my limited experience of when the car wouldn't start.

Thanks, that makes sense.

I just tried it again this morning.  The battery was in the bike and hooked up to the tender by the fixed cable.  The tender was saying that he battery was fully charged.  I disconnected the tender and the voltmeter read 12.4V across the battery terminals.  I turned on the ignition and left it for no more than about 5 minutes, after which it read 10.4V!  I tried turning the headlights on and it seemed to be struggling to trigger the relay on the lighting circuit.  I reconnected the tender and it was straight back in to charging mode, and has been for over an hour now, which seems excessive for the load I asked it to support for just a minute or two.

That does seem to tally with the process you describe, where a bad cell appears to charge to the full voltage but actually has only a tiny amount of charge capacity, which gets fully depleted very quickly.

There's no question that the battery is no longer serviceable, and it does look as if the tender is doing its best in the circumstances so can still be trusted.  Which is nice.

I did have another battery tender before the current one which I'm pretty sure did kill a battery. That brand seems to do well in group reviews online but I'm afraid I couldn't bring myself to buy another one from them, or recommend them to anyone else.