Testing the (green covered Internet) 3800 mAh battery
Hi, I have been doing some battery testing. I have a Watts Up meter, obtained from our own sales and wants page. I had checked it before and am confident in the numbers.
First, what is it? The unit can make concurrent measurements of current and voltage and watts and also time. This combined produces an absolute reading of amp hours or in other words battery capacity in one of the output figures.
I had done a more casual check of the Internet 3800 milli amp hour capacity cells previously mentioned and thought there had been a mistake, so I carefully charged the battery again and did a discharge test at around 1/2 an amp using a motor as the load. In theory the battery should have been able to run for at least 7 hours on this discharge current. Actual was 2 3/4. hours.
Remember that as the battery discharges the voltage of the battery reduces, it starts at about 7.9 volts and at below 6 volts it is about discharged. That is 1 volt per cell.
The results were very disappointing at total measured capacity of just 1445 mAh capacity, as against the claimed 3800 mAhrs capacity. (less than 40 % of claimed capacity). I took the load off and stopped the test when the motor was turning over at less than 2 watts.
Well I have 2 of these batteries and I had used them when new on a fastish model boat (a Bobby to those that know it) which planed nicely and took 4 amps under load with prop in the water etc. About 30 watts. Just one battery fitted and the run time was about 25 minutes, i.e not full speed the whole time. They both gave the same run time.
If you divide the measured 1.44 Amp hours by the current of 4 amps you come up with 21 minutes run time from the battery. So even when new the same capacity as I have just measured.
I was recently given some "clapped" out batteries all 7.2 volts and I got one good set out of a pair of 3000 mAh batteries. Not expecting a lot I used the same load as above and the new battery came out at 2450 mAh. Less than 10% loss of capacity over the years. I do not know what a high current discharge would show.
These cells were expensive from a well known supplier (Component Shop). They are probably 5 years + in age.
Like I said you get what you pay for.
Taking another view point you can probably buy 4 of the Internet batteries for the price of a one decent set of batteries.
You have to make your own decision there.
An interesting afternoon in the workshop.
regards to all, Roy