Prosecutors claim Lester fired two shots through a glass door with a .32-calibre revolver – hitting Ralph in the head and arm last Thursday.
Ralph then had to go to multiple homes to ask for help, and eventually found someone who would call 911.
While the teenager was being treated in hospital, he told police that the man had said: “Don’t come around here.”
Lester had turned himself in on Tuesday – and had agreed to relinquish his weapons, avoid contacting Ralph and his family, and have his mobile phone monitored.
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His swift release on $200,000 (£160,000) bail provoked anger and days of protests.
The pensioner has been charged with first-degree assault, and could face a maximum sentence of life in prison if convicted.
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He also pleaded not guilty to armed criminal action, an offence that can carry up to 15 years behind bars.
In his first court appearance, Lester walked up to the bench with the help of a cane and briefly spoke to the judge.
Prosecutor Zachary Thompson has said there is a “racial component” to the case, but hate crime charges have not been filed.
Civil rights leaders have been calling for the case to be treated as a hate crime – but according to Mr Thompson, Missouri laws mean this would carry a lesser sentence.
Ralph is now recovering at home – and his family says it is miraculous that he survived being shot in the head at point-blank range.
A GoFundMe page set up for his care has received $3.2m (£2.6m) from more than 87,000 donors.
At a rally, his lawyer Lee Merritt said: “A bullet travelled from [Lester’s] gun less than five feet into his upper temple, penetrated his skull, and they scraped bullet fragments off his frontal lobe on Thursday. On Saturday, he was home playing with his dog.”
Lester had told police that he lives alone and was “scared to death” when he saw a black man on his porch – and he thought someone was trying to break in.
But given Ralph is 5ft 8in tall, Mr Merritt argued he is hardly an imposing figure.
Experts believe Lester’s lawyers will claim self-defence under the state’s “stand your ground” law, which allows for the use of deadly force if someone fears for their life.
President Joe Biden has spoken to the teenager and his family, and tweeted: “No parent should have to worry that their kid will be shot after ringing the wrong doorbell. We’ve got to keep up the fight against gun violence.”
Over recent days, there have been several shootings involving victims who were mistakenly in the wrong place.
In Texas, a man shot and wounded two cheerleaders after one of them mistakenly got into his car – thinking it was hers.
And in New York, a 20-year-old woman was killed on Saturday night after the car she was riding in mistakenly went to the wrong address – and was met with gunfire in the driveway.