AA battery recharging

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tonyleigh

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With the widespread use of AA and AAA batteries in all sorts of equipment it seems logical to use a recharger through the 12v "cigarette lighter" socket. I notice high-speed 15min chargers are now available at reasonable prices. Batteries also appear to have different charging capacities (800 - 2300?). Are there any cautions to be aware of (safety, impact on other equipment drawing power bearing in mind it would only be used when under engine)? Is there any general advice regarding optimum battery capacity? Advice appreciated from those with knowledge/experience.
 
Beware of fast charge apparatus unless it has an auto cut-out. It is fastest way to vent and kill a rechargable.

Model shops and various sell 12v powered AA / AAA chargers that are set at the optimum 1/10th of capacity rating.

I have a speciality Model Shop job on the boat - designed specifically for two packs to charge at same or separate - 4.8V 4 cell + 9.6V 8 cell packs. These correspond to standard RC Model packs in Tx and Rx. The 9.6V is used to charge up VHF hand-helds at slow rate and is fine left literally indefinite. The 4.8V feeds a 4 cell carrier that I can put 4 AA's into.

You can even buy solar powered chargers for this job ...

Yes it's true that various items do recc'd not using rechargeables ... I believe based on :

Rechargeables have a flat line discharge and only when very close to full discharge does it drop very quickly - this confuses any battery power indicator on the item.
Second - a rechargeable will stay at or near its nominal voltage even under reasonable load ... about 1.1 - 1.2V and can discharge at high ampage rates ... I've known NiCd's catch fire / near explode when shorted with the ampage that they can supply ! A dry-cell will not sustain its nominal voltage very well when under load even though it says its higher at 1.5V than a Rechargeable .... typical can be as low as 1.0V or less when hard pressed.

I have used rechargeables in anything that takes AA's - no problem.
 
That is correct. NiCads and Ni-MH batteries are both lower voltage that conventional Alkali batteris. I believe 1.2V vs 1.5V. That means that a device expecting 6V from 4 AAs will only see 4.8V from fully charged rechargables. Some devices will not be happy.
 
Not strictly true IMHO as the 1.5V is no-load voltage and when item is switched on - most dry-cells will drop to similar or lower than a rechargeable.
 
Maplin do a good charger - 4 * AA & 4 * AAA with 12v and 230v adaptors for around £8.00. Taking it on board for my MP3 and the like. I seem to have so much electrical stuff on charge on the boat. A white flag will be popping out of the bat. housing soon!
 
I've been using rechargables for years on various boats - to the extent that the sign that I'm aboard is that a hand pops up whenever the engine goes on to plug in the recharger for my GPS, torch, walkman etc.

Made me most unpopular on a 7 week trip once where everybody else had a rucksack full of AAs for their bit of personal kit. Some serious calculating power (and many wasted hours) went into my final ultimatum to pay up for... 2 litres of diesel over the whole trip.
 
Re: AA cell recharging

I have a couple of chargers on board, one is primarily AA / AAA. The other charges all, AAA,AA,C,D,PP9. I bought it from Maplin on special at under £20. Not a fast charger but more useful, my other charger will charge 4 AA's in just under an hour. I would not go any quicker personally.

Click for link


We now have half a dozen D's to give 2 lots for the mag torch. I went through a phase of collecting rechargeable <u>cells</u> over winter and now have a big box on board. Should never have to buy cells again.

Another source for a charger is 7dayshop.com. Check out their cell prices, they have an own brand which I have so far been really happy with.

Hope this helps......
 
The higher capacity rechargeables leak charge at a higher rate.

Best not fit rechargeable batteries in seldom used emergency equipment.
 
Re: AA cell recharging

When a batt pack goes down - often its one cell only ... so its out with the stanley knife and break it open. Extract the tagged cells ... meter each one to see which is dud ... then charge up ... see which hold charge. In fact you can resurrect another same pack by subbing cells from one to other.
The cells that are good and don't go for other packs go into my supply bin for clocks, walkmans, making up own packs etc. etc. Only time I buy cells is when I want the extra capacity ones now available.
 
Tis indeed a good point, I have standard alkaline cells in my lifebuoy lights and alkaline AA's sealed in a bag in the grab bag for emergency VHF and GPS use. Though the h/h VHF and GPS usually have NiMh cells fitted.
 
I knew Ni-Cads had a lower voltage than alkalines, but didn't know that Ni-MHs did too - good to know. I use rechargeable alkalines. The brand in Canada is "Pure Energy" and they used to be sold in the US as Rayovac Renewal, tho' I don't know if they still are. They're 1.5v, last as long as ordinary alkalines between charges and can be recharged a few hundred times. They also don't "leak" their charge while sitting.

Kevin
 
I used the same Rayovac AA cells. You are correct, they don't leak their charge. Unfortunately they DO leak their electrolyte. I have a letter from Rayovac after I returned leaky cells to them. They suggested that I wasn't charging them properly and asked me which charger I used. It was one of their own chargers /forums/images/graemlins/confused.gif
I was sent replacements but always remove them from the battery compartment in case they leak too.
 
>Not strictly true IMHO as the 1.5V is no-load voltage

I would think that means it is strictly true! But whatever, it is true that different chemistries differ dramatically in their ability to deliver current. Notably Ni-MH can generally deliver a lot more than equivalent Alkaline batteries.
 
Re: Amp hours

I don't know anything about the voltage characteristic of all these battery types but I thought bog standard alkaline batteries won hands down in terms of amp-hour capacity?
 
Re: Amp hours

Yes, I think they do. But not in terms of peak current they can deliver for a short time.
 
Many thanks

Thanks, Guys. There is much food for thought in your replies and also the useful links. I feel much more able to proceed now and appreciate your advice.
 
Re: Many thanks

The simplest form of charger is a series resistor and a battery holder. You decide how fast you want to charge. Divide the time in hours into the capacity. 10 hours is the usual time which corresponds to a rate at which they may be charged long term without damage . Higher rates will damage the cell if not turned off after the charging period. 14 hrs at this rate will fully charge them.
So 2300 maH batteries require 230 milliamps. ( at 10 hr rate for 14 hrs) Decide how many cells you wish to charge and multiply by 1.2. So 4 cells is 4.8 volts. This voltage is subtracted from your 12 volts ships battery. (use 14volts if you have engine running). So for 4 cells you need to drop 12- 4.8 = 7 volts at 230 ma.
R=E/I R = 7 volts divided by .23 (amps) equals 28 ohms required in series with 4 batteries on 12 volt system. 30 ohms or even 47 ohms (a prefered value) will give you a simple safe charger. You can use a multimeter on current range to check to see if they are charging at a suitable current.
Incidentally the average cheap DVM introduces some significant resistance into the circuit on milliamp scale. This means that current will be higher than measured when the meter is removed (bypassed).
The resistor comes from Maplins RS orn similar. Use a 5watt rated resitor and it will get warm. olewill
 
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