Electronics 2000

Hi, that last post confused me, I have a few mins of batt now, I can read it. I thought the order of posts was different.
I have a tablet and mobile WiFi both use the same charger, when they are both flat at the same time all shuts down. I will sort out another charger sometime.

In order to predict how long the batts will last, I need to know how much power the device consumes, to do that I need the current (amps) drawn. If you have a ammeter or multi meter you can measure the current and draw conclusions.

Do you understand Ohms law?
Do you have a multi meter?

The volume goes up with voltage, so if the guy was running on 10 AA batts (15V) thats less than full volume... You hit the nail on the head...how long do the batteries last? Ask him or use a meter to find the current.

The problem with 20 AAAs ( apart from how long they last) is I am not sure if they will be slightly more than 1.2 V when fully charged... May be 1.3 V that's 26V total, that will probably be OK but ....it yours to fry you where warned.
Here's the warning... I would suggest 19AAAs that's 22.8V with a bit to spare.

Still I am not suggesting AAAs at all because I shouldn't think they will last long, but as I don't know how much power it consumes I cannot predict that.

Tar&stuff.

May be 15 D batteries.

That's a guess,

Get charger/chargers for D batteries.

My batt is a bit low I am going to charge for a bit.

Tar&stuff.

OK, having slept on it.
It depends on a number of factors, you sound young,(ish) if you learn Ohms law and get a £5 digi multi meter then you can understand and control your system.

Don't learn Ohms law and forget the meter and you are looking a 15 D or C rechargeable batteries and chargers....expensive.

Learn Ohms law and get the meter and you might choose a couple of motorbike batteries and a potentiometer, within the potentiometer/voltage divider you can tap any voltage up to about 28.8 V ( when the charger is on ) 25.6(ish( when charger is off and batts are fully charged)).
You say you want to keep price down such batts could be got very cheap or free from a scrap yard or refuse disposal place, small car batteries would do. Slight difficulty carrying them because they contain acid, some are sealed and can't leak unless you charge them till they explode. If you drop them you will burn your clothes and make your skin sore for a bit.
A charger will be about £5/8ish and a pot a couple or three quid.

Do not try this with out the pot as it might fry.

Tar&stuff.

http://www.ebay.co.uk/itm/Black-Motorcy ... 3f52575421

2 of those will run all day and may be night depending on the power consumed by the device.

Don't use with out a pot, I will find you one.

Tar&stuff.

http://www.ebay.co.uk/itm/Single-Turn-3 ... 1c55655633

You need a volt or multi meter so you can see what the voltage is and a charger, 24V or 12V.

Cheapest digi 10A multi meter on eBay.
http://www.ebay.co.uk/itm/DIGITAL-LCD-V ... 20d9d3a598
If you get one of those before buying the pot I can find a more suitable pot. That one will do but...

Tar&stuff.

http://www.ebay.co.uk/itm/Ansmann-ALCS- ... 43b782ce20

You might find a cheaper one.

Tar&stuff.

Another thing... If you are using 4 Ohm speakers you should not go above 20V.
With 8 Ohm speakers 24V is fine.

Tar&stuff.