Help Needed on Battery Selection

This is not a vehicle related issue, but I am hoping someone can help me. I have a homemade portable sterio system (4 speakers, amp, ipod) encased in a rolling cube cooler that currently runs off of an Optima deep cycle battery. It works great and lasts approx 12 hours before needing to be recharged. The Optima is 12v, 55Ah. However, the Optima battery is about 45 lbs, making the system quite heavy. I am looking to reduce the weight of my battery without significantly reducing my length of play. From my research, I believe that high amp hours are what I am looking for. I need a battery that can be charged and discharged over and over. I believe it has to be 12v to power the amp, but I am not 100% certain. Is there any kind of battery out there that will power my system for 10+ hours, can be charged and discharged repeatedly, and weigh less than 20-30 lbs? The lighter the better! Any help is MUCH appreciated.

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I hope you use it to make money, because the solution you seek is readily available, but it is not cheap! (Typical prices, depending upon options, will range $400 to $650)Go to "batteryspace.com" or telephone them, at 1-510-525-2328. They have lithium Iron Phosphte batteries that will perform BETTER than your present battery, at less than 1/2 the weight! (They have a 60 AH battery, weighing 22 pounds, with a higher operating voltage during discharge= better stereo performance!) These batteries are designed to be able to recharge about 2,000 times, which means they will last through about 10 to 20 times as many charge/discharge cycles as your present battery in your application. Because of this greater cycle life, the lithium battery is actually much cheaper in the long run!--If slightly shorter operating time is OK, they have a smaller battery, rated at 40AH, that weighs only 15 1/2 pounds. Either of these batteries will give better stereo power than your present lead-acid battery, due to the lithium battery operating voltage being closer to that in a car with the engine running, versus the lead-acid battery having a lower voltage. Much of the lithium battery operating time will be above 12.8 volts,(It starts out near 15 volts) whereas your present battery will quickly drop below this level, with most of its discharge ability below 12.5 volts.(starts out near 14 volts)-Bob Curry
PS:feel free to contact me for details/technical discussion.--301-439-3873

Robert M. Curry

Unfortunately, it does not make money but it does have a decent following that may contribute to its cause. Thank you VERY much for your help. I will research and be in touch with any questions. One question right off though, will the higher volts not hurt the amp, speakers, etc.?

NO, the higher voltage will not hurt, because normal voltage, in a car with engine running, is between 13.5 and 14.5 volts, and may reach 16 volts for short periods after starting on a cold day! Car stereo equipment works best at 13 to 16 volts, and performance gets poorer, with more distortion and less power available, as the voltage drops below 13 volts. (voltages above 16 volts ARE generally bad for equipment designed to operate on "12 volt" car systems) Typical battery voltage is 13.8 to 14.2 volts, with the engine running-go to your car, start it up, and measure it yourself!--Bob

Robert M. Curry

Themotorman's picture

NO, the higher voltage will not hurt, because normal voltage, in a car with engine running, is between 13.5 and 14.5 volts, and may reach 16 volts for short periods after starting on a cold day! Car stereo equipment works best at 13 to 16 volts, and performance gets poorer, with more distortion and less power available, as the voltage drops below 13 volts. (voltages above 16 volts ARE generally bad for equipment designed to operate on "12 volt" car systems) Typical battery voltage is 13.8 to 14.2 volts, with the engine running-go to your car, start it up, and measure it yourself!--Bob

Be very careful about changing to a LiFePo4 system. You might have many more problems that you want at a very great cost too. I suggest you stick with SLA for a while the LiFePO4 technology is changing fast and next year will be much better for reliability and news. BTW a small Honda very quiet gas powered generator will provide tons of power at a much lower weight and also be totally portable. I know gas powered stuff is not a choice that we V types like but sometimes the solution is simpler than we think too!

building the future... one crappy Lipo at a time!!

I have been actually USING a Li-Fe-Po4 battery from "Batteryspace.com" to power the accessories on my VECTRIX for months! This 20 ampere-hour battery, supplied with its built-in battery management/equalizing board, which has separate power leads for charging and discharging, and cost me about $295.00-I charge it using a 10 ampere, 15 volt regulated power supply, and it powers my XM satellite radio, power amplifier, subwoofer, electric gloves, emergency siren/horn, 2 way radio, and auxillary lights! This battery is mounted under the seat, and performs very reliably for the typical 2 hour or less discharge cycle of the VECTRIX, as the motor battery fails before the accessory battery. My operating voltage seems to be around 13 volts for the majority of the time, giving very good performance. Do not attempt to use lithium batteries without some means to assure equal charging and voltage limiting during charge. (Buying the battery with the board included is the easiest, but in my case, the board limits discharge current to 40 amperes maximum, which is fine for my usage) This battery is not much bigger/heavier than the 7 ah lead-acid battery that was previously used, but works better/longer!--Bob Curry

Robert M. Curry

Thanks. I'm not sure that battery will last long enough for me, but will you please post the link from batteryspace.com? Not being sure what I am looking for, I couldn't find what you're talking about.

The web address is "batteryspace.com"--go there, and they have a 12.8 volt lithium iron phosphate battery, part number CU-J220, with a ID number of 5128. This battery, using 4 Thundersky 40 ampere-hour cells, wioth a matching charger, charge/discharge control board, and discharge protection, sells for $529.85, and weighs only 14.5 pounds! Maximum current availability is 30 amperes thru its charge control board, if your system exceeds 30 amps, you would have to call them on the telephone, and arrange to have the control board modified for your current level. I sent you much of this info previously, along with MY telephone, so any questions could be resolved. (301-439-3873 is MY number)--I assure you, this battery, or one of the others they have available, would be a big improvement for your system, with longer service life, and lighter weight. (these batteries will fully discharge/recharge over 1,500 times, your present battery would be lucky to last 200 discharge/recharges, therefore this battery is actually CHEAPER in the long run!)--Bob Curry

Robert M. Curry

I have a simpler approach but its add odds with everyone else here who like complex solutions

From somewhere like Yesa you can get 40ahr Lifepo4 cells and individual 3.3v chargers (cost $80 - $100 each)
so four of these will cost $400

connect them in series but when you charge them put individual small 5amp charger on each, so that will need a strip of 4 chargers but you never have any balancing problems. Each charger stops when their cell is full.
Just make sure you dont run cells right down to nothing (but people over worry about that too much aswell, they are still well recoverable even if they get to 2 v before you notice which is unlikely)

Yesa cells can do 5c no probs (i.e. 5x40 =200!) so you can get more than enough current. I reckon the 40amp cells will do about the same time as what u use now, (and take about 7hrs max to recharge) but in total they will only weigh 5kg.
to recap forget fancy electronics, just put the 4 cells in a block together (connected with copper strips) but clip the crocodile clips on each individual cells when you charge.
I await my flaming from the likes of Bob lol!

To Colin: FLAME ON!--No, not a flame, but for only $129.85 more, he would get a "ready-to-use" pack, with a USA warranty, that already is assembled, using matched "THUNDERSKY" cells, including a CHARGER, short circuit, over discharge, and charging protection built in.--To many users, this may be worth the extra money.(The 15.5 pound weight INCLUDES everything!) --Bob

PS: While 3.3 volt supplies are plentiful, because 3.3 volts is used in the computer world, that voltage is a little LOW to fully charge most Li-FE/PO4 cells, and voltage around 3.65 volts per cell proves to give more useful discharge capacity.

Robert M. Curry

Thanks for the input guys. Unfortunately, I don't think I will be able to justify either of these options right now, as I do have a working battery, just not the ideal one. I'll probably have to stick with the one I have until it dies, then look to upgrade to the lithium option.

Given my lack of battery knowledge, the "ready to use" option is probably my safest bet, but thanks again for the suggestion.


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