Rechargable Batteries Question

Ebe_Scrooge

Over the years I've amassed a selection of rechargable batteries - mostly AA size. They've got different ratings, e.g. 1600mAh or 2000 mAh. The question is, does it matter which charger I use ? The first set I got were a set of 4 x 1600 mAh with a charger included. Then my digital camera came with 2 x 2100mAh with their own charger. I'm also probably going to buy some more high-capacity ones shortly. If I, say, charge the 2100 batteries in the charger that came with the 1600 batteries, will it charge them fully, or do you need to have a charger that's matched to the batteries ? If it doesn't matter that's great news, as the batteries themselves are pretty cheap and I've already got several chargers I could use, so I don't need to buy another charger.

isofa

You just need to charge the higher capacity ones for a longer period, as long as they are they same type/voltage.

So if say you charge the1600mAhs AAs for 4 hours to fully charge them, charge the 2000mAhs AAs for 5 hours etc. Have a look at the output of the charger and you can roughly work it out, it won't hurt to charge them a bit longer, but don't charge them for tens of hours longer.

cowbutt

It depends on the design of the charger. Essentially there are three types of charger:

- dumb chargers
- timer-controlled chargers
- delta V (aka "ΔV") chargers

The first type is essentially just a mains transformer, taking 240V AC and turning it into DC. This type is the cheapest around, and will overcharge batteries if they're left on charge too long. These chargers tend to be quite slow (upwards of four hours charge time).

The second type uses a timer to limit full-rate charging time before switching to a safe 'trickle charge' mode, meaning that as long as the batteries used are the right capacity for the charging rate, they will never be overcharged. If the capacity is too low, they will be overcharged. If the capacity is too high, they will be undercharged, unless the charging process is restarted with the partially-charged batteries. Of course, that brings the possibility of overcharging!

The third type is the best as they detect the characteristic small drop ("Delta") in voltage ("V") when NiCd and MiMH batteries are fully charged. They switch to a trickle charge mode when the battery is fully-charged, no sooner or later. Ideally, each battery in the charge set is monitored individually, and if the charger is "fast" (two hours or less for ~1600mAh batteries) then a fan and thermal protection is good to have.

If the charger never switches to a trickle charge mode, assume it's the first type. If it does, but it's not explicitly described as the "delta V" type, it's safest to assume it's only timer-controlled. If you've got a number of sets of batteries of different capacities, a good delta V charger is a wise investment (see Maplin or Tantronics).

theartfullodger

There's a recent very illuminating article here
http://www.reghardware.co.uk/2009/05/07/beginners_battery_maintenance/
about recharging batteries. It is about Laptop batteries but the principles are the same.

Until I read it I hadn't realised what an impact temperature has.

Cheers!


Lodger

Ebe_Scrooge

Thanks for all the helpful replies :-)

isofa

theartfullodger wrote: »

There's a recent very illuminating article here
http://www.reghardware.co.uk/2009/05/07/beginners_battery_maintenance/
about recharging batteries. It is about Laptop batteries but the principles are the same.

Until I read it I hadn't realised what an impact temperature has.

Li-Ion behave very differently to NiMh and older NiCads... They are essentially very unstable, and temperature is a crucial factor.

In fact completely draining a NiCad was essential to get a long life out of them, charging at a fuller rate, made their "memory effect" reduce the capacity. Luckily there aren't many NiCads about nowadays, NiMh are much more efficient and barely suffer from "memory effect".

cowbutt

isofa wrote: »

Li-Ion behave very differently to NiMh and older NiCads... They are essentially very unstable, and temperature is a crucial factor.

In fact completely draining a NiCad was essential to get a long life out of them, charging at a fuller rate, made their "memory effect" reduce the capacity. Luckily there aren't many NiCads about nowadays, NiMh are much more efficient and barely suffer from "memory effect".

NiCd batteries are still commonly used in 'cordless' power tools, though higher-end power tools are starting to use Li-Ion batteries, but they all have different advantages and disadvantages in this type of device - http://www.content4reprint.com/technology/making-the-power-tool-battery-decision-nimh-vs-nicad-vs-li-ion.htm

isofa

cowbutt wrote: »

NiCd batteries are still commonly used in 'cordless' power tools, though higher-end power tools are starting to use Li-Ion batteries, but they all have different advantages and disadvantages in this type of device - http://www.content4reprint.com/technology/making-the-power-tool-battery-decision-nimh-vs-nicad-vs-li-ion.htm

True, but all ours are LiIon (all bosch), older electric toothbrushes also use them, but better expensive models don't. NiCads are a real pain!