By way of background -  I built a small incubator controller for my father
a few years ago. It uses a PIC 628A and monitors the temperature inside the
incubator using a DS18B20. Two heating elements (basically ceramic light
globes) are turned on / off via a solid state relay. A simple 2 x 16 LCD
displays the current temperature and target temperature. Last year I added
an under temperature alarm as both of the ceramic elements blew at the same
time (as the do not emit light it is quite possible that one of the ceramic
elements was blown for some time and then the other blew).

As part of the "upgrade program" for this year I am trying to add some
additional functionality:

1. My father lives in an area that has occasional power outages so I would
like to add a simple battery back up that allows the monitoring of the
supply voltage. Intent is to provide an audible alarm if supply voltage is
interrupted (and perhaps an indication of how long it has been off). I want
the system to be a simple as possible so I was thinking of some sort of
NiCads on a trickle charge? I have seen some real cheap LiIon batteries on
DealExtreme etc but the charging requirements seem to be a lot more
complex. Is there a simple option for these types of cells?

2. Although there are two heating elements, there is currently no simple
way of determining if both are working. I was thinking of some sort of
current drawn monitoring circuit that could visually indicate that the
heating element is working. Another option may be to put another
temperature sensor on each element but I was hoping for a simpler option.
The heating elements are 240VAC / 60 W.

The whole controller fits into a small box about 150mm x 75mm so there is
not much room for additional hardware.
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