[Dujon]

Saturn c,

I'm with the others on this. I would never recommend using a battery charger to run any equipment - they are not designed for that purpose and often have significant amounts of ripple (i.e. varying voltages) on their output. Doug's suggestion of attaching it to a SLA battery is sound, though even then it's possible to measure small amounts of ripple (this is probably not important in your case).

What do the specs for the heq5 say when it comes to current requirements? This is important for two reasons:

A) To run it off a battery you can get a rough idea as to how long any given battery will last before going flat by dividing the battery's amp-hour (Ah) rating by the current used by the unit. If the unit is only used intermittently then, obviously, the life of the battery charge will be extended.

B) If you do decide to use a battery with charger attached it will give you some idea as to battery life, even if the battery charger itself is providing less than the unit is using. This, of course, means that the battery charger will be working at full stretch during the use of the equipment and will also need to be used to 'top up' the battery after your observing session, which means you might need a reasonably robust charger.

Incidentally, allowing a sealed lead acid battery to run completely flat is not a good idea and can result in its demise.