Battery size is really going to be determined by your choice of motor. Steppers
will need higher capacity batteries than DC motors.

Nickel Cadmium (NiCd) cells are rechargeable with a terminal voltage
of 1.2v per cell. They are capable of quite high current delivery. Selecting
the correct type can allow currents of several amps from an AA sized cell
(not for long though). NiCds can be recharged between 500 and 1000 times
with care and are cheap in the long run for the power to weight they offer.
When selecting NiCds shop around as capacities vary quite considerable
for similar looking cells. Typical high street shop AA cells may be only
600mAh capacity when you can find cells the same physical size with 950mAh

A selection of cells:

  • AA alkalines
  • AA NiMH
  • AA NiCd
  • PP3 NiCd

NiMH cells are like more expensive NiCds and have, perhaps, twice the
capacity but cannot deliver such high currents. Nevertheless, an AA cell
can still deliver a couple of amps without too much strain. This really
should not be a problem in a micromouse even if you are driving powerful
stepper motors.

In fact, if you need the full current delivery of a NiCd, you have probably
got a drive system that runs on steam generated by an electric heater
– now there’s an idea :).

NiMH cells are available in all the same physical sizes as NiCd cells
and can often be used as drop-in replacements. They share the same 1.2v
terminal voltage per cell which is constant through most of the battery
life the difference is in the capacity. It is not hard to find AA size
NiMH cells with 1500mAh capacity and AAA cells at 700mAh.

Dry cells (alkaline) have higher voltages and relatively huge capacities
– probably twice that of NiMH. Too expensive for use during development,
they are not necessarily a bad choice for a competition run if you are
desperate. Watch out for poor voltage regulation during discharge though.
There are circumstances where dry cells, in spite of their apparent high
capacity, appear to last less long than rechargeable cells.

Rechargeable alkaline manganese cells have recently become available
at about twice the price of non-rechargeable alkaline cells. These boast
at least 25 charge-discharge cycles – more if they are not allowed to
completely discharge before being recharged. Terminal voltage is 1.5v
rather than the 1.2v of NiCd and NiMH cells. Special chargers are needed
for these cells.

Approximate sizes and capacities for a range of off-the-shelf NiCd cells:








1/3 AA




2/3 AA








4/5 AF




2/3 AF








A less common alternative is the sealed lead acid battery. These are
most commonly used in burglar alarms and are available in a range of voltages
and capacities. They can deliver very large currents but suffer an overwhelming
disadvantage in terms of weight. Think of them as just like a small car
battery and you will get the idea. In spite of the clear penalties, one
of the UK’s most well known mice, Maisie, uses a 12 volt sealed lead acid
accumulator for energy storage.

More exotic technologies exist and are used in things like camera batteries.
Ready assembled battery packs and fast chargers are available – at a cost.

A low current, DC motor driven mouse might be able to use the small but
expensive non-rechargeable 6v Lithium Manganese Dioxide batteries used
in some 35mm cameras. For example, the 2CR5 battery is 17mm x 34mm x 45mm,
weighs only 37g and has a capacity of 1300mAh. Alternatively, a pair of
CR2 cells at 3v 750mAh each. These are 16mm x 27mm and weigh only 11g.
Finally, there is a PP3 package giving 9v 1200mAh

If you are really keen, you could try a couple of tagged Lithium Thionyl
cells. These are very expensive but offer 3.7v per cell in a C size package
(26mm dia x 50mm length) with a capacity of 8000mAh. While only good for
about 180mA discharge rates, they will keep you mousing for about 44 hours
non-stop at that rate.

This Post Has 2 Comments

  1. pret83

    Hi. How much watts is the power consumtion of a micromouse in average? I’m considering the usage of supercapacitors, but maybe the size and the weight is the issue. 100F capacitors are quiet large for a micromouse and by my calculations 4 of them needed – on voltage drop from 10V to 5V to produce cca 300Ws.

  2. Peter Harrison

    This is just a very rough estimate (more a guess really) but…

    For a classic micromouse, of mass 120g, using faulhaber 1717 motors, and assuming the mouse is always acclerating or decelerating at about 4m/s/s while travelling at 1m/s, I would guess that you would expect currents of about 1.2A ans a peak electrical power of around 8 Watts.

    Since the mouse is not spending all its time at full tilt, average during a run might be less than half that.

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