Hi all,

I have a BT Synergy 3100 cordless DECT phone and needed to get some new batteries for it, because the old ones don't take much charge any more.

I opened the back of the handset to find it took 2x AAA 1.2v rechargeable batteries, so I went down to Maplin and bought a pack. I swapped them out and put the handset on the base. The charge light came on, but the handset stayed dead... I assumed this might be the case. I have now left the handset charging for well over 12 hours, but still there is no life.

Have I done something wrong? Do the batteries need to be recharged on a proper mains charger, or have I bought the wrong batteries? The only difference I can see with these new batteries is that they are rated at 1000mAh and the old ones are 550mAh. I thought this would be okay because surely it just means they have a bigger charge capacity?

Can anyone help please?

Thanks!

:-Joe

Please don't think I'm being facetious but have you double checked the batteries are inserted correctly? It's always possible to get it wrong if the little graphic on the phone isn't very clear.

If the batteries are inserted correctly there's no reason why they shouldn't take at least some charge - unless one or both is faulty.

Do you have any other rechargeables you could try? (Don't try with non rechargeables as they can leak badly if you try and charge them).

Or any other device you could try the new batteries out on to see if they do have any charge?

There are several types of rechargeable battery. Perhaps most common are NiCad and NiMH. They have slightly different charging characteristics and a charger designed solely for one type might not work too well with a different type of battery.

So check out the labels on the batteries and make sure they are the same type. If they are the same type then the phone charger should eventually charge them up.

Hi,

Both the old and new batteries are NiMH...

Well that eliminates one problem.

I wonder if the charger is actually working? perhaps the reason the old batteries were not holding a charge wasn't because they were old and at the end of their useful life but because they were not being charged properly?

If you get a mains charger you could test that. If you put the old batteries in the mains charger then put them in the phones and get a decent life out of them then the batteries may be OK and the charger in the phones is cream crackered.

That's what I was fearing... Having to buy yet more stuff! I only really bought the batteries because they were half-price...

I think if I buy a mains charger, they usually come with batteries too, which is a bit of a waste. I'd hate to buy a mains charger and find they still don't work.

Maybe first I will try cleaning the connectors on the base and handset, perhaps they've got a bit dirty. Surely if the handset wasn't charging, I wouldn't be able to recharge the old batteries every time they went flat?

Cleaning the terminals might help. If you have a nail file or similar then that can cut through any corrosion and gunge down to the metal.

The charger may be only partially charging the batteries rather than not charging at all. As I say the only real way is to try charging the batteries in an alternative charger. If they hold a better charge then the phone charger is on it's way out. if they don't hold any better charge then the batteries are dead.

You can get chargers on their own, for example...

http://www.maplin.co.uk/Module.aspx?ModuleNo=115119

Thanks for the link... That's another £13 on top of the £5 I spent on the batteries though. I can buy a whole new DECT base and handset for about £20... I will consider the charger as a last resort

But just to confirm, sounds like I do have the correct batteries, yes? There are many websites selling replacement batteries for the Synergy 3100 and they appear to be identical in spec...

OK, sorry if this is really obvious, but does the handset have a power button? On mine I can turn it on/off.

According to the manual for this phone that I found online the batteries are Ni-MH so if the replacements you have got are also Ni-MH then they ought to work.

But you said the charge light came on so it's unlikely to be the connection. Plus the old batteries did take a bit of charge.

Can you put the old batteries back and see if they still charge?

Then try one old and one new in various combinations.

You do occasionally get completely dud rechargeables and if one of the new ones is o/c (or very high resistance) then the pair will not function at all.

Yes, they still appear to be working okay. (but only last for about 20 minutes when in use).


Should I really be mixing old batteries with new? Especially if they have different mAh ratings?


I did buy a pack of four, and only two are needed... I could try the other two new ones, or combinations of them?

Try the other two first. If they charge up OK then one or both of the others could be duff. If the other pair do not charge up then you either have a duff set of batteries or the charger is faulty.

Swapping batteries around to see if you can find any two of the four that work is one option. Bit of a faff though. Some stand alone chargers however can indicate if one or more batteries in a set is not charging correctly.

It's a pain to fault find this sort of thing. You really need a known good set of batteries or a known good charger to compare with. If the charger is faulty you will never work out if the batteries are faulty or not if you do not try a set you know work properly when in another unit. Or you have a working charger to see if that can charge the batteries you are testing.

OK, so the charger is OK and the contacts are ok.


It's quite safe. Not a good idea for actual long term use as they will only perform as well as the worse of the pair. Certainly OK as a diagnostic.


Absolutely. Try the other pair first.

Based on the information you have given I suspect that they will work.

Think about this, OP. In normal use, you may never switch your phone off, and so may not even know how to switch it back on.

On mine, it involves holding down the button used to clear a call for several seconds. There is nothing labelled on/off.

ETA: Ah. You say you've put the old batteries back in and they work. Disregard previous advice!

I assume the battery contacts are identical? I have come across special variants before now.

As he's just verified that he can still charge his old batteries it's now unlikely to be this.

Plus he said that the 'charge' light came on.

This may sound silly, but some batteries are wrapped in a plastic so tight you don't obviously see it. Take a very close look at the batteries and see if this is the case.

Thanks all... I will check it out again tonight when I get home and let you know.

Hi all,

Well I got it sorted! It was basically "human error"... I took the batteries out, and wondered if they were making contact properly... neo_wales - you mentioned about being wrapped in plastic, so I checked for that and even though they weren't, the plastic seals at the top were a bit thick, so I trimmed them back a bit. Also, because the other batteries had been in the phone for so long, the metal springy strips at the terminals had been pretty much flattened back... So I got a knife and carefully pulled them out again so they could make proper contact.

And hey presto... As soon as I stuck the new batteries back in, the phone jumped back to life!

Thanks for everyone's helpful suggestions here... Job done!

Cheers

:-Joe

Glad to know you got it sorted out.

Incidentally, the "charge" light is complete rubbish... It even lights up when I put the handset on the base with no batteries in it.

It presumably means 'there's power available to charge'.

My phones have the 'charging' icon blinking all the time when they are on the base.

It's actually quite annoying as you get used to the screen having something blinking all the time and don't notice when the answering machine has a message.