We offer the backups as a one time purchase for new customers who have not had the chance to purchase their own yet, we do not have a supply of replacements or batteries for the units that we sell, once they are purchased from us they are completely customer-owned devices.
Guys, surely you must realize that, on the surface, that sounds really
lame. The batteries eventually wear out -- PSI only rates them for a ten year lifespan and, for the most part, doesn't do direct sales, instead going through resellers and (*ahem*) service providers.
That said... I just visited PSI's product page for the PS18L-U2
, and I find it just a little weird that nowhere do they quote battery capacity in milliamp-hours. They mumble something about 18 Watts continuous power, but don't actually mention a specific time or capacity at that power draw. 18W at 12V is 1.5 Amps. So if the eight hour claim is based on a 1.5A draw, that suggests a battery capacity a bit north of 12000mAh, which is in the ballpark for a LIon battery of that physical size. However, the data sheet for the Adtran 411 ONT
claims that the power draw is less than 4 Watts, which is 333mA at 12V. So dividing 12000mAh by 333mA gives us 36 hours.
Obviously the only way to be sure about any of this is to test it.
[Edited: My previous arithmetic was wrong.]