user53840: I have posted this in a few places, so sorry if you have seen it somewhere else
Im working on a battery powered led strip project,
iv put the project together and have been testing with a mains power supply
Iv run some tests and found at max I'd be pulling 4.5 amps
Averaging around 2 ish

I rounded out to about 3.5 amps, and said for 90 mins run time id be looking at the 7ah battery
7/2 = 3.5 so 2 hours runtime 
I got a 7ah SLA 12v battery, running though a 12v to 5v converter to power the led strips
(Arduino is running off a usb battery pack)
However after about 45 mins I tested the battery and it said 10.9 v
Which I understand to be too low for SLA batteries (11 should be the minimum?) so I shut it off
My question is did I mess up somewhere and get my math wrong?
Many thanks in advance

user62523: There are a few things that may contribute to your lower than expected battery lifetime.
Effective capacity: you should aim to never use more than 50% of the capacity of a lead acid battery or you will shorten its lifespan considerably.
Also, note that lead acid battery capacity is usually given for a discharge time of 20 hours (C20 rating). The “C” rating could be different but its value should be on the label of the battery.
In the case of a stated capacity of 7Ah at C20, this means the capacity has been calculated at a discharge rate of 7Ah/20h = 350mA. For higher discharge rates, such as in your application, the effective capacity will be much lower.
Battery voltage: measuring battery voltage under load does not say much. Measure the battery voltage “at rest”, when completely disconnected from the load for about 1 hour.
Charging: Are you charging the battery with a proper charger?

53840: <p>I have posted this in a few places, so sorry if you have seen it somewhere else</p>
<p>Im working on a battery powered led strip project,<br>
iv put the project together and have been testing with a mains power supply<br>
Iv run some tests and found at max I'd be pulling 4.5 amps<br>
Averaging around 2 ish<br>
<br>
I rounded out to about 3.5 amps, and said for 90 mins run time id be looking at the 7ah battery<br>
7/2 = 3.5 so 2 hours runtime <br>
I got a 7ah SLA 12v battery, running though a 12v to 5v converter to power the led strips<br>
(Arduino is running off a usb battery pack)<br></p>
<p>However after about 45 mins I tested the battery and it said 10.9 v<br>
Which I understand to be too low for SLA batteries (11 should be the minimum?)<br> so I shut it off<br></p>
<p>My question is did I mess up somewhere and get my math wrong?<br>
Many thanks in advance</p>
 62523: <p>There are a few things that may contribute to your lower than expected battery lifetime.</p>
<p><strong>Effective capacity</strong>: you should aim to never use more than 50% of the capacity of a lead acid battery or you will shorten its lifespan considerably.</p>
<p>Also, note that lead acid battery capacity is usually given for a discharge time of 20 hours (C20 rating). The “C” rating could be different but its value should be on the label of the battery.</p>
<p>In the case of a stated capacity of 7Ah at C20, this means the capacity has been calculated at a discharge rate of 7Ah/20h = 350mA. For higher discharge rates, such as in your application, the effective capacity will be much lower.</p>
<p><strong>Battery voltage</strong>: measuring battery voltage under load does not say much. Measure the battery voltage “at rest”, when completely disconnected from the load for about 1 hour.</p>
<p><strong>Charging</strong>: Are you charging the battery with a proper charger?</p>
