# Portable backup battery question. **URL:** \ **Category:** Factual Questions\ **Created:** [January 23, 2009, 6:38pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680 "2009-01-23T18:38:39Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Nobody](https://avatars.discourse-cdn.com/v4/letter/n/94ad74/32.png) [@Nobody](https://boards.straightdope.com/u/Nobody)\ **Post date:** [January 23, 2009, 6:38pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/1 "2009-01-23T18:38:39Z")
If I have a ventilator [humidifier](http://www.google.com/search?complete=0&hl=en&q=fisher+paykel+hc500&btnG=Google+Search) with the following specs: Supply voltage -------------230V±20V ----------------------------------115V Supply Frequency----------50-60Hz Supply Current-------------0.8A max at 230V --------------------------------1.5A max at 115V Heater Wire Capacity------60W Water Heater----------------85W And I plug it in to [this](http://www.amazon.com/Xantrex-XPower-Powerpack-Portable-Backup/dp/B000157TP8), how long could the backup battery run it? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 23, 2009, 6:49pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/2 "2009-01-23T18:49:59Z")
From their manual: > [@](#): > > Table 3-1AC Appliances and Run Times > AC Appliance Wattsa > Hoursb > Cordless telephone (stand by) 5 40 > Home security system 5 40 > Clock radio 8 22 > Portable stereo 10 17 > Fluorescent work light 14 10 > Fireplace fan 20 8 > Laptop computer 25 6 > Table lamp 40 3 > Color TV – 13" 60 2 h 30 min. > 3/8 “ drill 190 20 min. It looks like your device draws a maximum 165 Watts or so, so the 20Ah battery in your backup battery unit should power it for just under an hour. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 23, 2009, 7:09pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/3 "2009-01-23T19:09:52Z")
> [@beowulff](#): > > It looks like your device draws a maximum 165 Watts or so, so the 20Ah battery in your backup battery unit should power it for just under an hour. That’ll drain the battery dry, and even a deep cycle AGM will give up the ghost after a few rounds of that. Half an hour is probably about the longest he’d want to ever let it run between recharges. ---
**Author:** ![IAmNotSpartacus](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@IAmNotSpartacus](https://boards.straightdope.com/u/IAmNotSpartacus)\ **Post date:** [January 23, 2009, 11:15pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/4 "2009-01-23T23:15:11Z")
> [@beowulff](#): > > From their manual: > It looks like your device draws a maximum 165 Watts or so, so the 20Ah battery in your backup battery unit should power it for just under an hour. The unit draws 1.5 amps. The battery has 20 amp-hours of capacity. How exactly did we arrive at an hour’s worth of power here? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 23, 2009, 11:18pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/5 "2009-01-23T23:18:01Z")
> [@IAmNotSpartacus](#): > > The unit draws 1.5 amps. > > The battery has 20 amp-hours of capacity. > > How exactly did we arrive at an hour’s worth of power here? 20Ah at **12v**! So 20 x 12 = 240Wh With losses, figure on about an hour of runtime. ---
**Author:** ![IAmNotSpartacus](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@IAmNotSpartacus](https://boards.straightdope.com/u/IAmNotSpartacus)\ **Post date:** [January 23, 2009, 11:26pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/6 "2009-01-23T23:26:21Z")
Ah, clearly I overlooked it was giving the capacity at DC and not AC voltages :smack: ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [January 24, 2009, 12:02am UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/7 "2009-01-24T00:02:59Z")
Yup, and DC to AC converters typically run at about 85% efficiency. If you’re running a CPAP or anything similar off a convertor, you’ll be needing a 150+ amp hour deep cycle battery to get more than a single nights use. AFAI can tell, Fuel cells are not yet an option. ---
**Author:** ![Nobody](https://avatars.discourse-cdn.com/v4/letter/n/94ad74/32.png) [@Nobody](https://boards.straightdope.com/u/Nobody)\ **Post date:** [January 24, 2009, 2:51am UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/8 "2009-01-24T02:51:11Z")
I actually don’t own the portable battery. My wife is on a ventilator and is hooked up to a humidifier. She has it set up, so she can hook the ventilator to the back of her electric wheelchair and draw power from the wheelchair battery. The company that worked on hooking up her ventilator did so before she got her humidifier, and after she got it, they refused to work on a way to attach it too. We are also able to put the humidifier on to the back of her wheelchair, but it can’t be hooked up to her chair. Unless we use, what’s unofficially called, an artificial nose, instead of the humidifier, she really isn’t able to travel freely around the house. I was hoping maybe to buy a portable backup battery, strap it to her wheelchair, and plug the humidifier into that. That way, she could have freedom to travel around the house, but it seems that if the 400 unit only lasts 1/2 hour, then even the 1,500 watt unit would only probably last a couple of hours. Oh well. ---
**Author:** ![Gus\_Handsome](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@Gus\_Handsome](https://boards.straightdope.com/u/Gus_Handsome)\ **Post date:** [January 24, 2009, 2:00pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/9 "2009-01-24T14:00:36Z")
I had one of those once. One night during a power outage I plugged in a 14 inch TV/VCR combo and started watching “Planes, Trains, & Automobiles” on VHS. There I am thinking I’m “all that and a box of cheeze” having the luxory of watching a movie while the entire block is in darkness, hehe. I got about 45 minutes in when the battery died. No more movie for me! I think those little back-up jobbies are great if you want to plug in a cell phone, or very low voltage light, but for anything big, forget about it. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [January 24, 2009, 3:17pm UTC](https://boards.straightdope.com/t/portable-backup-battery-question/482680/10 "2009-01-24T15:17:57Z")
> [@Gus\_Handsome](#): > > II think those little back-up jobbies are great if you want to plug in a cell phone, or very low voltage light, but for anything big, forget about it. Don’t forget, the maximum battery capacity decreases over the lifetime of the unit. So a 3yo unit, even fully charged, may only have 50% of its originally rated capacity.