Reddit reviews Portable DC 12V 4500mAh Rechargeable Li-ion Battery for CCTV Camera Wireless Camera / Baby Monitor, Digital Camera, CD/MD

OK lets avoid the bluetooth speaker in general.

Micca MB42x +Lepai 2020 +Bluetooth adapter +12V battery(for the beach just put everything in a bag)

80+20+20+20 = $140

• Keep in mind the author of that video doesn't seem to know much electronics either. "Pulse Wave Modulator." The "low voltage hurts motors but slow PWM is good" bit is bullshit. It's AC motors that melt when the voltage is too low.
  
  
• Most DC motors like those are totally symmetric in operation forward and backward. They have a positive and negative lead because they need to specify which direction it goes w.r.t. input polarity.
  
  
• Swapping the power switch and pwm controller will work... the problem is that the PWM controller probably always draws a little bit of power if it's powered up, even if it's turned down to zero or no motor is connected. It will run down the battery when turned off.
  
  
• I am pretty sure the diode is not required if you use a PWM unit designed for motors. If you use one intended for a resistive load like a light bulb, then yes, you would definitely need it.
  
  
• Driving cheap motors with high frequency PWM can be a bit sketchy at times... their brushes make a lot of noise, and you can't put big diodes caps on them because the PWM will melt them.
  
  
• When I search for "12v li-ion battery" on amazon I get a lot of cheaper options, like this. YMMV. Some of them look a bit sketchy. You could also use an SLA battery, but it's heavier for the power. But you don't need a lot of power.
  
  
• The drill chuck is kinda ridiculous, and probably half the total weight. I guess if you don't have access to a lathe to make yourself a proper spool and can't find one online you have to improvise...
  
  
• If I were designing this -- and almost certainly how all the professionally designed ones are built -- it would use a motor with an optical encoder. That would have the benefit of not changing speed due to variable friction or battery voltage, and would be able to do fast and slow movement with the same motor. Doing that from scratch is probably well in excess of your electronics skills, but there's probably an arduino sketch of something similar out there.
  

one of [these,](http://www.amazon.com/Portable-4500mAh-Rechargeable-Battery-Wireless/dp/B008UKKXRC/ref=sr_1_3?ie=UTF8&qid=1405463569&sr=8-3&keywords=12v+rechargeable+battery+pack
) and one of these and your good to go. trust me.

http://www.amazon.com/Portable-4500mAh-Rechargeable-Battery-Wireless/dp/B008UKKXRC/ref=sr_1_3?ie=UTF8&qid=1397599005&sr=8-3&keywords=12v+lithium+battery

This will last all day long
http://www.amazon.com/gp/product/B008UKKXRC/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Non-mobile: this

^That's ^why ^I'm ^here, ^I ^don't ^judge ^you. ^PM ^/u/xl0 ^if ^I'm ^causing ^any ^trouble. ^WUT?

Similar to this. Its not great quality though and I've never had a chance to fully test battery life yet but I think it would last at least 4 hours on full volume continuously.

Yep. That's the stuff. I'd reccomend this battery to accompany it. http://www.amazon.com/Portable-4500mAh-Rechargeable-Battery-Wireless/dp/B008UKKXRC/ref=sr_1_10?ie=UTF8&qid=1375231869&sr=8-10&keywords=12v+rechargeable+battery

Boosting up to a 12 volt from a 3.7v batter strains the battery pretty heavily. power is the same on both sides of the converter minus efficiency losses, so this would require 3 times the current on the low side.
Typically, a battery's mAh rating is tested under specific loading conditions. Puekerts law states that drawing too fast from a battery can change its actual capacity by a greal deal (maybe 40%).

I would use a 12v battery like thishttp://www.amazon.com/Portable-4500mAh-Rechargeable-Battery-Wireless/dp/B008UKKXRC/ref=sr_1_4?ie=UTF8&qid=1418685970&sr=8-4&keywords=12v+lithium+ion+battery+pack#productDetails

then use a buck converter to step down to the led voltage. you can even buy a buck converter IC to make it simple. The IC will regulate the output, although LEDs arent terribly sensitive to voltage fluctuation

[Here is a better option] (http://www.amazon.com/HitLights-Rechargeable-3800mAh-Lithium-Connector/dp/B007RQW5WG/ref=sr_1_1?s=hi&ie=UTF8&qid=1405311237&sr=1-1&keywords=12v+lithium+battery), in my opinion. Or [this] (http://www.amazon.com/Portable-4500mAh-Rechargeable-Battery-Wireless/dp/B008UKKXRC/ref=cm_cr_pr_product_top) I would also take a look at building your own battery pack [similar to this] (http://www.amazon.com/ExpertPower%C2%AE-3500mAh-Extended-Battery-iRobot/dp/B007V6UL1Y/ref=sr_1_95?ie=UTF8&qid=1405311619&sr=8-95&keywords=14.4v+battery). The first two look like they might even plug right into your amp.

Heck even [this] (http://www.amazon.com/12v-Standscan-Battery-Power-Pack/dp/B00BTGTJPG/ref=sr_1_4?s=electronics&ie=UTF8&qid=1405312250&sr=1-4&keywords=12v+portable+battery) would work better and be cheaper/lighter if you put some rechargeables in it.

I would want any battery pack around 12-15V. I would also consider getting a [cheaper amplifier] (http://www.amazon.com/LP-2020A-Lepai-Tripath-Class-T-Amplifier/dp/B0049P6OTI/ref=pd_cp_e_0). It uses the same amp chip (ta2020) as the one you posted

Edit: Essentially, I wouldn't want to carry around 7 pounds of lead acid batteries when I could carry much lighter batteries to do the same job.

oh ok sweet. then I could keep a pack charging and a pack on my backpack. I sometimes spend 6 to 8 hours wearing it so its important to either have a long battery life or quick charging/battery swapping. getting the weight down would be awesome.

Are these the batteries you tested as working fine on the lepai?