I have a lot of power outs and when there is power a have a low voltage not enough to charge my UPS batteries, as a result my UPS can supply me with only few minutes instead of 6 to 7 hours.
what I have is a UPS with 2 12 v lead acid bat. and extra 2 bat. ,I want to by pass the step up transformer and feed the router and nanostation with 0.6 A @ 9 v and switchable 0.8 A @ 15 v / 0.3 A @ 24 v. There is no problem to start from scratch or to manipulate the originals as the method is simple and can be executed by a monkey and easy to maintain and repair " i'm not an engineer ".
Thanks...

 

Basic off the shelf voltage bucking converters would easily let you run your 9 and 15 volt devices off o f a shared 24 volt battery set.

But you still need to address the problem of how you will get the batteries charged. Dead batteries don't do any good regardless of what they are running.

If you electrical power is active but the voltage is lower than what it's normally supposed to be you can get solid state battery chargers or DC power supplies that have wide input voltage ranges that would help with charging things way faster than the UPS unit's built in charging system can do.

Multi Stage charging would be best but for low cost most any SMPS (Switch Mode Power supply) unit that can be adjusted to run at ~14 - 14.5 volts will work just fine as a 12 volt battery charger. Same with higher voltage one that can be adjusted to work in the 28 - 29 volt range for a 24 volt battery set.

Amp output wise if regular power drop out are a common problem you may what to go with a unit that can supply at least the same amp output as your combined battery bank Ah (Amp-Hour) rating is which if you have a fairly large 100 Ah battery bank that could require a fairly large 100+ amp capacity power supply to get recharge times down under 1 - 2 hours in worst case situations.

 

thanks for the good advice.
one of the problems is that I can't find off shelf voltage regulators so I had to build one" many actually", they work fine from the batteries but first they seem to drain the batteries pretty fast and second they don't work on the UPS out to the batteries which I hooked the circuit to, I think the ripple is the problem although I hooked about 300 uf capacitors and a 1n4007 diode to a 7815 and 7809 each.
and regarding the power supply I was thinking of off shelf car battery charger"I may build a Li-ion pack" but I have to convert the charger to a UPS and smooth the output to run the nanostation which seem very sensitive to ripple.
by the way,,, is it possible to hack the POE adapter to recieve 24v DC instead of 220v AC.??!!
sorry for making this long.

 

Us knowing your battery Amp-Hour capacity would go a long way.
Same with your location. If you have internet you more than likely have local mail delivery too.

An automotive battery charger would work fine provided it's rated to run at whatever low line voltage you may be experiencing. If not then it won't do a bit of good if your line voltage drops more than a few percent below the chargers input voltage rating.

No you can't hack a 220 VAC power pack to work on 24 VDC.

There's no such ting as too many words here. Most often the problem is too few.