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I use some audio devices (mixers and effect boxes) that literally drains out my 9v cells (specially the rechargeable). I'm thinking on doing arrays of LiIon batteries (rated at 3.7v-4000mAh each), but not sure the amount of batteries in series will 'mimic' the behavior of a common 9V. Could it be a 2 cell series array = rated at 7.4 V ?? which I'm thinking this may suck-up more power and reduce the performance of batteries) or it Could be a 3 cell array = 11.1v!! ?? I'm affraid this could fry my circuits the second I plug it in.

Any comments, are really appreciated.

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    \$\begingroup\$ Can you be more precise about the devices you want to power? I'm thinking of guitar pedals but I might be wrong. The point is that probably your devices can easily handle the 12V of a fully charged 3s LiIon, and they can probably make it with the 8V of a 2s one. \$\endgroup\$ Apr 23 '14 at 14:22
  • \$\begingroup\$ Do they use a single 9v or multiple in each? \$\endgroup\$
    – Passerby
    Apr 23 '14 at 17:54
  • \$\begingroup\$ If you have a USB battery bank, you can use this to get 9V, it also comes with 9V battery connector. kickstarter.com/projects/femtocow/usb-912 \$\endgroup\$
    – Cano64
    Oct 28 '15 at 13:30
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The answer depends quite a lot on the device you're powering. Many modern electronics use a linear voltage regulator which provides the operating voltage from the input voltage. This type of device often has a fairly wide range of acceptable input voltages - a 5V regulator like the LM7805 can provide a regulated 5V output with an input voltage between 7V and 35V. The regulator will draw the same current from the supply as the load draws (generally less than 1A) and dissipate the excess power (obeying P=IV) as heat. A voltage below 9V is very unlikely to damage your device, so you could probably try it and see.

What this means is that there's probably a voltage range with which the device will work happily. If there's no specification or manual which defines this, opening up the device and inspecting the power input of the PCB would probably reveal a voltage regulator of some sort. You could look up the datasheet for this to get a better answer. Remember that if you do choose a voltage above 9V, the amount of heat generated in the regulator will increase, which could cause it to fail if it was already being operated towards the current limit.

There's another consideration which has to be made when using lithium batteries - safety. Deeply discharging lithium batteries can permanently damage them and even present a fire hazard. You can buy lithium battery packs which incorporate small ICs to automatically cut them off when the voltage drops too low.

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The output voltage of lithium ion batteries varies over their discharge cycle a great deal more than alkaline batteries. You need to find out what range of voltages are safe for your equipment and match that. Alternatively, you could use a switching regulator to produce 9 volts from a battery pack that is either always higher than that (use a buck regulator) or always lower than that (use a boost regulator). What is the current draw of your equipment? If it is not too high you could use a linear regulator to get 9 volts from a three cell stack and recharge when the cell voltage falls to 3 volts each. This would, of course, waste some power and give you shorter battery life than a switching regulator.

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  • \$\begingroup\$ Audio equipment and switchers, not going to play nice in your ear \$\endgroup\$
    – Passerby
    Apr 23 '14 at 17:53
  • \$\begingroup\$ Well, not if you don't design the switch-mode regulators properly, no, but if you know what you're doing it will be just fine. Have you heard of class-D audio amplifiers? If they work passably well, then I think we can conclude that switched-mode systems and audio are not mutually exclusive. \$\endgroup\$ Apr 24 '14 at 0:59

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