DC Battery Stability

I have a 12 V load that works by connecting an adapter from the AC socket and this adapter output 12v to the load. I decided to make a 12 v battery that can charged and the feed this load , all the work is done perfectly but the problem is that the battery when connected to the load its output voltage varies from 12 til 0 and the increase and continues like that, which may damage my load, so i think i should use a voltage regulator that outputs 12 v but it will work? if yes what kind of regulators i can buy?? Note : the load takes 1.2 A and the batteries are 4000 mAh

• I'm having trouble understanding your question, could you add a schematic? But: if I'm understanding it right, it sounds like you want a 12V-to-12V step-up/step-down regulator with at least 1.2A output current? – Hearth Oct 28 '18 at 17:25
• If your battery voltage is going all the way to zero, though, you have some bigger problems than just regulating the output. – Hearth Oct 28 '18 at 17:26
• you're going to have to give more details on the load. The battery voltage going to zero indicates that your battery is being periodically short-circuited which is not a good thing. – Hearth Oct 28 '18 at 17:42
• The load is a university project that needs 12 v and it worked properly when i fed it with an adapter (12v, 3A), this load consists of many circuits that used as a students manual for using amplifier...but if there is a short-circuit, why is the load working properly with the adapter, and if the short-circuit is from the battery, why the indications are true when testing the battery without load and the voltage is stable 12v?? – user202574 Oct 28 '18 at 17:47
• Can you give a schematic of your load and how you're connecting the battery to it? – Hearth Oct 28 '18 at 17:48

I would use a 8.4V LiPo battery pack rather than 12.6V.
An 8.4 will would use a DC-DC step-up boost converter.
A 12.8V would require a combination step-up/step-down converter.
Off the shelf solutions are few for a 1.2 A, 12V - 12V chargers and regulators.

But you already have a 12V battery pack.

You could use the versatile Linear Tech LT3652 Battery Charger

Input voltages from 5V to 32V Will charge up to 2A
Works with Lead Acid, Li-ion, LiPo, and Li-phosphate.

Example 8.4V Li-ion charger powered with 12V AC adapter:

Example 12V Lead Acid charger powered with 5 VDC to 32 VDC :

Then for the output regulation the Linear Tech LTC 3111 12V 1.5A Buck-Boost DC/DC Converter
With low battery shut off.

If you want to switch between the AC adapter and battery without the voltage dropping to zero you can use a Linear Tech LTC4358 Ideal Diode Switch .

Or a Linear Tech LTC4412 Automatic Switch