Instruction: Answer the given question by extracting information from the supporting document.

Input:
Question: Can a 2nd battery be kept in the charger for an indefinite period or will that ruin it?
Document: I have to agree with other reviews; the second battery should be included in this price range. I almost had Hoover convinced of this but their answer was that this device packaged for a short period in some test markets with two batteries but for whatever reason, the strategy wasn't working for Hoover.I'll keep it and use it but I think I may have kept looking or opted for the second battery if I knew what I learned after using it and calling Hoover about it.
This Stick Vacuum Cleaner is amazing. We had a Swiffer Vac before and recently tried out the Electrolux Ergorapido and this is definitely better. We use it on our ceramic floors and hardwood with no issues. It is extremely powerful and maintains a charge for as long as we need it. To prolong the battery, make sure and it remove it from the vacuum when not in use and also don't leave it on the charger for a long period of time.You can't go wrong with HOOVER! !
This is a nice vacuum that works well when everything is new and the battery is charged. We bought this unit as a 'between cleanings' vacuum to keep our floors swept. To that end, we used it about once a week. It does a good job on area rugs and bare floors and will run for about 10 to 12 minutes before the battery is drained.The weakness of this product is the battery and charger. If you're lucky, the charger will fail within the warranty period.
This is supposed to indicate that the charger is reset. Nevertheless, the battery would not begin charging - no blue steady led. Reading deep into the comments here, we found a person who puts their charger on a timer that cuts power to the charger after 3 hours. That sparked an idea. Maybe the charger needs to be unplugged for a longer period of time to allow some internal voltage measuring circuitry to fully bleed down and truly reset itself.
Standing up by itself is fine, but I would have liked to be able to hang it up.- The battery charger is a standalone unit that must be kept on a horizontal surface.- It is recommended that you do not store the battery in the charger. If the battery is overcharged - it will shorten battery life. Clearly not the best charger design.
I had purchased this item through Amazon warehouse (used). When I received the item, the charger and the battery did not work. I contacted Hoover and they took care of the problem for me. Now it works beautifully. I had to wait a few days for the new battery, but their customer service was wonderful. The vacuum is nice and light, perfect to do the stairs. I may just have to buy a 2nd one for the downstairs level.
I ordered the extra battery so I can always have a fresh battery waiting. I have two little dogs that come in and out all day and I can keep the floor/rugs grass free with little effort. I also like that the vacuum does not have to be kept on a charger. The battery comes out and goes right into the charger.
Seriously, I bought this, charged it overnight - then used it for about 14 minutes. 2nd charge and use was 10 min or less then no battery. There are no instructions - should I leave the "charged" battery in the vacuum, out of the vacuum, in the charger all the time??? Total waste. Also was not that simple to put together. A real bummer. Why did so many people give the 4-5 stars? Ease of use and life of charge are TERRIBLE!
I have had this a few months and love the way it works. The problem is the battery charger quit working. I bought another battery charger for $40! and that one didn't work out of the package! So now I have this great little vacuum that won't work because I can't charge the battery! If the battery charger kept working, I would have given this 5 stars. It's so nice and lightweight and easy to maneuver on the stairs.
And, since we purchased it through Amazon they would not offer a refund. By this time the Amazon refund period had expired.So, we contacted the Hoover headquarters to see what they could do. The assured us that they would put a replacement charger in the mail that day. It is now early April and no sign of the promised replacement.Bottom line is, if yours works that is great. But if you need Hoover customer support, God help you because they surely won't.
Answer: I have done this since I  bought the vacuum about 1 1/2 years ago.  But I have had problems after 6 months of use with each of the three batteries I have owned. After  6 months the battery wouldn't charge anymore. I have called Hoover and done the charger tests with them, and the charger works fine. But the batteries wear out. I use the  Hoover at least twice a day for cat hair and crumb pickup.  The vacuum is  well  designed and picks up well.  If only the company could make a battery that lasts.  These are expensive batteries and they are warrantied for two years. This is the one disappointing aspect about the vacuum. Otherwise I love the vacuum.