Battery Time & Stats

How long time does it take to recharge a rechargeable battery?

Timeline of Battery History. 1748—Benjamin Franklin first coined the term 'battery' to describe an array of charged glass plates.; 1780 to 1786—Luigi Galvani demonstrated what we now understand to be the electrical basis of nerve impulses and provided the cornerstone of research for later inventors like Volta to create batteries. Remove the battery, once you feel a loss of power from the tool. Do not tape the trigger ON. Let the battery sit out of the charger for a least 2 hours until the battery is at room temperature. Place the battery in the charger overnight to allow for a full charge on each individual cell (A minimum of 8 hours at room temperature). This is perhaps the most popular in the lot due to its simplicity. This free battery.

Formula for calculating batteries charging time :
hr = mAh / mA
“hours” equal “battery size in milliampere-hour” divided by “charger output power in milliamperes”
(Need more information? The charge formula is explained in details with examples further below.)

Charging rechargeable batteries.

Type into the calculator your rechargeable battery’s capacity number, normally can be red on the battery body e.g. 1700 mAh ( milli-ampere-hours ). Then select the battery type/size in the left column ( NiMH – NiCd – AAA – AA – C – D – 9V ( 9 volt )) and in the right side select a current output ( electric power output ) of your charger in mA ( milli-amperes ).

Type in a capacity number of one battery only. Without changing outcome as per hours/mA a 1-4 batteries can be charged.

You can select and use a specific / special battery sizes at the bottom of the field and then set a different current output from a battery charger, if needed, by choosing the 1mA current and multiplying the outcome backwards – dividing in fact by the existing current value at which your charging equipment operates.

Re-charging 9 volt rechargeable batteries

Time control for charging of common 9V rechargeable batteries ( NiCd and NiMH 9 V batteries.) The timer takes longer because these can only be charged at much lower current rate of 0.1C or 1/10C ( mAhr/10 = charging time in hours ) of their mAh capacity value. Usually between 30 mA to 100 mA depending on the 9V battery capacity in mAh. This is still great to put up with considering that the 9 volts non rechargeable batteries cost arm and leg, but they don’t have to.

Trickle charge, continuous charging method

This is done with a very low charging current to keep the battery or batteries constantly alive, same like with a cordless phone battery pack that is docked in its station base.

Lets do the life/live charging examples, but before still in a short theory to clear some practical terminology out from the way.

Common abbreviations – symbols – prefixes

The International acronyms one will possibly come across with while using batteries and their changers:

nickel-metal hydride ( cell ) – NiMH
nickel-cadmium battery ( cells ) – NiCd
9 volts battery – 9V – 9 V
milliampere hour – milliamp hour – mAh – mAhr – mAhrs
milliampere – mA ( 1/1000 of ampere | 1 A = 1000 mA )
ampere – A ( electric charge amount measure )
battery current or capacity – C
hour – h – hr
hours – hrs

How do I calculate charging time for rechargeable battery manually ?

Formula for manual calculation for battery recharging processes
AAA – AA – C – D sizes rechargeable batteries:
hours ( charging time ) equals to 12 x Ahr = hrs OR 12/1000 x mAh = hrs
( 12/1000 x mAh = hours of charging )
Example calculations with this manual formula; calculate charging time length for 2400 mAh NiMH AA size 1.2v rechargeable batteries with 100 mA charger and secondly with a 3.5 times more powerful 350 mA current output power charger:

100mA battery charger:
12 : 1000 = 0.012
0.012 x 2400 = 28.8 (hrs)
It requires 28.8 hours ( 28 hours and 48 minutes ) to charge or recharge aa size 2400mAh batteries with charger that has 100mA current output.

350mA battery charger:
12 : 1000 = 0.012
0.012 x 2400 = 28.8
28.8 : 3.5 = 8.2 (hrs)
It takes 8.2 hours ( 8 hours and 12 minutes ) time to charge or recharge 2400mAh batteries with charger that has 350mA current output.

Here is a second example of how long to charge batteries but this time for charging 1800 mAh 1.2 volt NiMH aa type rechargeable batteries and with the same current chargers:

100mA battery charger:
12 : 1000 = 0.012
0.012 x 1800 = 21.6 (hrs)
It takes 21.6 hours ( 21 hours and 36 minutes ) to charge or recharge aa size 1800mAh batteries with charger that has 100mA current output.