I have a battery charger that requires batteries are charged in pairs. However I have a wireless keyboard that uses three batteries. Is there a (safe) way I can charge all of the batteries at once?
I usually have to go through two sets before I can charge the 'lone pair', but I often misplace the one that's waiting.
If it helps, the device is a Duracell CEF14UK
I suggest rotating the batteries through the charger. If it takes two hours to get a full charge on two batteries, that would be 120 minutes. Total time to charge 3 batteries would be 50% more than that or 180 minutes. Put batteries in the charger for one-third of the 180 minutes which woulds be 60 minutes. Remove the battery from the left. Move the one from the right to the left. Move the extra one into the right position. Do that three times and the three batteries will each be charged the required amount of two hours.
There's no (known) hack for this -- you should buy a better charger, that can charge any number of batteries at the same time; anything else probably isn't worth the effort, probably isn't safe, and could damage your batteries. See here and here for more info on why this is so.
I had this same problem (but with three-cell LED headlamps). Finally gave up and bought a charger (LaCrosse BC-700) that would charge 1-4 batteries - and a mix of AA and AAA cells, too. More than worth the $35-40 cost in eliminated aggravation.
Take a rechargeable battery out of some other device in the house, and charge it
No other rechargeables in the house? Buy or obtain (places like supermarkets have battery bins where old batteries can be put for recycling. Someone is bound to have thrown a rechargeable away by mistake) another battery. If you're good at losing batteries but good at not losing chargers, secure the battery to the charger using string and electrical tape so you have an accessible battery to make up the pair any time you need to charge an odd number of batteries
I concur with other comments on this page that you should NOT attempt to bridge the terminals of the empty slot with wire, screws etc because it's quite likely your charger is charging a pair of batteries in series and doing this would see the lone battery be destroyed as the charger will forever try to charge it to make it reach the ~2.5volts it expects a pair to be, and it'll never get that high. If this charger is charging in series pairs, charging a single battery with double the voltage could be a fire risk
I also concur with comments that you should buy a better charger that can charge an odd number of batteries/charge independently; battery charging in series works well when both cells are functional and effective but if one cell is degraded the other one suffers
First of all, do NOT just short circuit the battery charger with a piece of foil to force it to charge your battery individually. Looking at the spec sheet provided, your charger outputs 3V to each pair of batteries to charge them in series. If you place a single battery in the charger and force it to charge, then your charger will be supplying 3V to a 1.5V battery and end up destroying it.
However, you can still use this charger if you are very careful. Instead of short circuiting the other battery terminals, place a resistor in them to slow down the current. Use a 10 ohm resistor and attach it to the terminals. Then you can carefully monitor the battery as it charges to make sure it doesn't overvolt. You will need to check it frequently until it reaches capacity and then remove it before it gets destroyed.
(inspired by @subjectivist's and @caius-jard's answers)
increase your supply of rechargable batteries and rotate their usage.
e.g. with four batteries you can charge all 4 → use 3 → when they're done, you're left with 1 charged and 3 uncharged → charge 2 → 3 charged ready for use + 1 uncharged waiting for the next chance to charge → when the batteries are empty again you have 4 uncharged batteries ready to charge all 4. You might want to use a different battery to be waiting for usage so they all have similar number of duty cycles.
If I counted correctly, with 7 batteries you could even manage to have near zero down time on battery change (i.e. whenever the batteries you're currently using, there will be at least three batteries ready to use so you can just swap and continue using the keyboard.
It would probably require another life hack to keep track of which battery had the most duty cycles.
The safe bet, although a bit more expensive, is to use 6 batteries:
This will ensure uniform proper charging / discharging cycles for all batteries.
There might me a slight concern that some batteries will stay dis-charged for some time, until the next 3 batteries get used. This should be acceptable though, as nothing in the world is perfect.
On the other hand, there are portable devices which use only one battery - hopefully you have one of those. Pair the keyboard to that device, maybe manage to have all 4 batteries discharged at (more or less) the same time.
I've never had this exact problem, but occasionally I've had to make fake batteries out of aluminum foil. This will just send the electrical signal back to the circuit and keep it running.
How to make it:
This method has been safe for me and the aluminum foil has lasted pretty long (I've had one for about 6 months). Just make sure to turn of the charger before removing the fake battery.
If you have one battery less for charging to use battery pair charger, Use a metal screw as a replacement. It is a good conductor.
