Here is a summary, by PICAXE Forum poster Ibenson, based on work done by a number of people:
Low-power features-several techniques suggested in previous posts to reduce PICAXE power.
1. Run at slower speed. Poke the OSCCON register ("poke$8f,%00000000") to run at 31.250kHz instead of 4mHz (1/128th the speed).See "08M UNDER clocking"--
http://www.picaxeforum.co.uk/showthread.php?t=2233 ; also
http://www.kranenborg.org/ee/picaxe/ (search for low-power) also search the forum for "OSCCON".
2. Run DISABLEBOD. This turns
off a PICAXE brown-out detection, which normally causes an 08M to shut itself off at a bit below 3V. With DISABLEBOD, 08Ms have been kept alive down to 1.3V. See manuka, et. al.:
http://www.picaxeforum.co.uk/showthread.php?t=6513 ; also Mycroft2152, "Low PowerPICAXE 08M - BOD" --
http://www.picaxeforum.co.uk/showthread.php?t=4826
3. If you are using occasional ADCs while on battery, turn off the ADC module between reads by poking the ADCON0 register ("poke $1f,value"). Bit0 of value turns it off, but the register should be read first so that other bits are preserved. Quote Dippy "
So for low-power people (doing the occasional A/D) it looks like a quick poke might be in order to switch off ADC module" http://www.picaxeforum.co.uk/showthread.php?t=5950 ; also
http://www.picaxeforum.co.uk/showthread.php?t=8346
4. Pull down all unused inputs to 0V, e.g. with 100K or even 1M resistors. See "problem with getting very low power consumption"
http://www.picaxeforum.co.uk/showthread.php?t=2292
Quote (Kranenborg)
"After I had tied all 18X inputs low current consumption dropped from a very unstable 250 uA to a very stable 30uA at 5V and 31kHz (equiv. current consumption at 4MHz is approx 1.5 mA = 1500uA thus meaning a reduction to only 2% of the original consumption)".
5.Current-limit any outputs to the degree possible. For example, at 4.5V, an LED with a normal 330 Ohm dropping resistor uses about 13 mA. With a 22k resistor it is much dimmer,but still readable, & uses only ~.2 mA. Newer ultrabright LEDs drawing such sub mA currents can often be viewed at some distance, & at ~1mA may be almost blinding. LED "blink patterns" can further reduce overall current usage while expanding the information provided.
NB: For any register poking, confirm via Microchip datasheets that you're poking the correct one for that chip!